Reorganize packages, closes #79

- All packages go into either cmd or pkg directories - Most packages renamed - Server packages moved into pkg/server - sanitize moved into webui, as that's the only place it's used - filestore moved into pkg/storage/file - Makefile updated, and PKG variable use fixed
2025-12-17 17:47:03 +00:00 · 2018-03-09 19:32:45 -08:00
parent f00b9ddef0
commit f8c30a678a
55 changed files with 225 additions and 220 deletions
--- a/pkg/server/smtp/handler.go
+++ b/pkg/server/smtp/handler.go
@@ -0,0 +1,628 @@
+package smtp
+
+import (
+	"bufio"
+	"bytes"
+	"container/list"
+	"fmt"
+	"io"
+	"net"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/jhillyerd/inbucket/pkg/log"
+	"github.com/jhillyerd/inbucket/pkg/msghub"
+	"github.com/jhillyerd/inbucket/pkg/storage"
+	"github.com/jhillyerd/inbucket/pkg/stringutil"
+)
+
+// State tracks the current mode of our SMTP state machine
+type State int
+
+const (
+	// GREET State: Waiting for HELO
+	GREET State = iota
+	// READY State: Got HELO, waiting for MAIL
+	READY
+	// MAIL State: Got MAIL, accepting RCPTs
+	MAIL
+	// DATA State: Got DATA, waiting for "."
+	DATA
+	// QUIT State: Client requested end of session
+	QUIT
+)
+
+const timeStampFormat = "Mon, 02 Jan 2006 15:04:05 -0700 (MST)"
+
+func (s State) String() string {
+	switch s {
+	case GREET:
+		return "GREET"
+	case READY:
+		return "READY"
+	case MAIL:
+		return "MAIL"
+	case DATA:
+		return "DATA"
+	case QUIT:
+		return "QUIT"
+	}
+	return "Unknown"
+}
+
+var commands = map[string]bool{
+	"HELO": true,
+	"EHLO": true,
+	"MAIL": true,
+	"RCPT": true,
+	"DATA": true,
+	"RSET": true,
+	"SEND": true,
+	"SOML": true,
+	"SAML": true,
+	"VRFY": true,
+	"EXPN": true,
+	"HELP": true,
+	"NOOP": true,
+	"QUIT": true,
+	"TURN": true,
+}
+
+// recipientDetails for message delivery
+type recipientDetails struct {
+	address, localPart, domainPart string
+	mailbox                        datastore.Mailbox
+}
+
+// Session holds the state of an SMTP session
+type Session struct {
+	server       *Server
+	id           int
+	conn         net.Conn
+	remoteDomain string
+	remoteHost   string
+	sendError    error
+	state        State
+	reader       *bufio.Reader
+	from         string
+	recipients   *list.List
+}
+
+// NewSession creates a new Session for the given connection
+func NewSession(server *Server, id int, conn net.Conn) *Session {
+	reader := bufio.NewReader(conn)
+	host, _, _ := net.SplitHostPort(conn.RemoteAddr().String())
+	return &Session{server: server, id: id, conn: conn, state: GREET, reader: reader, remoteHost: host}
+}
+
+func (ss *Session) String() string {
+	return fmt.Sprintf("Session{id: %v, state: %v}", ss.id, ss.state)
+}
+
+/* Session flow:
+ *  1. Send initial greeting
+ *  2. Receive cmd
+ *  3. If good cmd, respond, optionally change state
+ *  4. If bad cmd, respond error
+ *  5. Goto 2
+ */
+func (s *Server) startSession(id int, conn net.Conn) {
+	log.Infof("SMTP Connection from %v, starting session <%v>", conn.RemoteAddr(), id)
+	expConnectsCurrent.Add(1)
+	defer func() {
+		if err := conn.Close(); err != nil {
+			log.Errorf("Error closing connection for <%v>: %v", id, err)
+		}
+		s.waitgroup.Done()
+		expConnectsCurrent.Add(-1)
+	}()
+
+	ss := NewSession(s, id, conn)
+	ss.greet()
+
+	// This is our command reading loop
+	for ss.state != QUIT && ss.sendError == nil {
+		if ss.state == DATA {
+			// Special case, does not use SMTP command format
+			ss.dataHandler()
+			continue
+		}
+		line, err := ss.readLine()
+		if err == nil {
+			if cmd, arg, ok := ss.parseCmd(line); ok {
+				// Check against valid SMTP commands
+				if cmd == "" {
+					ss.send("500 Speak up")
+					continue
+				}
+				if !commands[cmd] {
+					ss.send(fmt.Sprintf("500 Syntax error, %v command unrecognized", cmd))
+					ss.logWarn("Unrecognized command: %v", cmd)
+					continue
+				}
+
+				// Commands we handle in any state
+				switch cmd {
+				case "SEND", "SOML", "SAML", "EXPN", "HELP", "TURN":
+					// These commands are not implemented in any state
+					ss.send(fmt.Sprintf("502 %v command not implemented", cmd))
+					ss.logWarn("Command %v not implemented by Inbucket", cmd)
+					continue
+				case "VRFY":
+					ss.send("252 Cannot VRFY user, but will accept message")
+					continue
+				case "NOOP":
+					ss.send("250 I have sucessfully done nothing")
+					continue
+				case "RSET":
+					// Reset session
+					ss.logTrace("Resetting session state on RSET request")
+					ss.reset()
+					ss.send("250 Session reset")
+					continue
+				case "QUIT":
+					ss.send("221 Goodnight and good luck")
+					ss.enterState(QUIT)
+					continue
+				}
+
+				// Send command to handler for current state
+				switch ss.state {
+				case GREET:
+					ss.greetHandler(cmd, arg)
+					continue
+				case READY:
+					ss.readyHandler(cmd, arg)
+					continue
+				case MAIL:
+					ss.mailHandler(cmd, arg)
+					continue
+				}
+				ss.logError("Session entered unexpected state %v", ss.state)
+				break
+			} else {
+				ss.send("500 Syntax error, command garbled")
+			}
+		} else {
+			// readLine() returned an error
+			if err == io.EOF {
+				switch ss.state {
+				case GREET, READY:
+					// EOF is common here
+					ss.logInfo("Client closed connection (state %v)", ss.state)
+				default:
+					ss.logWarn("Got EOF while in state %v", ss.state)
+				}
+				break
+			}
+			// not an EOF
+			ss.logWarn("Connection error: %v", err)
+			if netErr, ok := err.(net.Error); ok {
+				if netErr.Timeout() {
+					ss.send("221 Idle timeout, bye bye")
+					break
+				}
+			}
+			ss.send("221 Connection error, sorry")
+			break
+		}
+	}
+	if ss.sendError != nil {
+		ss.logWarn("Network send error: %v", ss.sendError)
+	}
+	ss.logInfo("Closing connection")
+}
+
+// GREET state -> waiting for HELO
+func (ss *Session) greetHandler(cmd string, arg string) {
+	switch cmd {
+	case "HELO":
+		domain, err := parseHelloArgument(arg)
+		if err != nil {
+			ss.send("501 Domain/address argument required for HELO")
+			return
+		}
+		ss.remoteDomain = domain
+		ss.send("250 Great, let's get this show on the road")
+		ss.enterState(READY)
+	case "EHLO":
+		domain, err := parseHelloArgument(arg)
+		if err != nil {
+			ss.send("501 Domain/address argument required for EHLO")
+			return
+		}
+		ss.remoteDomain = domain
+		ss.send("250-Great, let's get this show on the road")
+		ss.send("250-8BITMIME")
+		ss.send(fmt.Sprintf("250 SIZE %v", ss.server.maxMessageBytes))
+		ss.enterState(READY)
+	default:
+		ss.ooSeq(cmd)
+	}
+}
+
+func parseHelloArgument(arg string) (string, error) {
+	domain := arg
+	if idx := strings.IndexRune(arg, ' '); idx >= 0 {
+		domain = arg[:idx]
+	}
+	if domain == "" {
+		return "", fmt.Errorf("Invalid domain")
+	}
+	return domain, nil
+}
+
+// READY state -> waiting for MAIL
+func (ss *Session) readyHandler(cmd string, arg string) {
+	if cmd == "MAIL" {
+		// Match FROM, while accepting '>' as quoted pair and in double quoted strings
+		// (?i) makes the regex case insensitive, (?:) is non-grouping sub-match
+		re := regexp.MustCompile("(?i)^FROM:\\s*<((?:\\\\>|[^>])+|\"[^\"]+\"@[^>]+)>( [\\w= ]+)?$")
+		m := re.FindStringSubmatch(arg)
+		if m == nil {
+			ss.send("501 Was expecting MAIL arg syntax of FROM:<address>")
+			ss.logWarn("Bad MAIL argument: %q", arg)
+			return
+		}
+		from := m[1]
+		if _, _, err := stringutil.ParseEmailAddress(from); err != nil {
+			ss.send("501 Bad sender address syntax")
+			ss.logWarn("Bad address as MAIL arg: %q, %s", from, err)
+			return
+		}
+		// This is where the client may put BODY=8BITMIME, but we already
+		// read the DATA as bytes, so it does not effect our processing.
+		if m[2] != "" {
+			args, ok := ss.parseArgs(m[2])
+			if !ok {
+				ss.send("501 Unable to parse MAIL ESMTP parameters")
+				ss.logWarn("Bad MAIL argument: %q", arg)
+				return
+			}
+			if args["SIZE"] != "" {
+				size, err := strconv.ParseInt(args["SIZE"], 10, 32)
+				if err != nil {
+					ss.send("501 Unable to parse SIZE as an integer")
+					ss.logWarn("Unable to parse SIZE %q as an integer", args["SIZE"])
+					return
+				}
+				if int(size) > ss.server.maxMessageBytes {
+					ss.send("552 Max message size exceeded")
+					ss.logWarn("Client wanted to send oversized message: %v", args["SIZE"])
+					return
+				}
+			}
+		}
+		ss.from = from
+		ss.recipients = list.New()
+		ss.logInfo("Mail from: %v", from)
+		ss.send(fmt.Sprintf("250 Roger, accepting mail from <%v>", from))
+		ss.enterState(MAIL)
+	} else {
+		ss.ooSeq(cmd)
+	}
+}
+
+// MAIL state -> waiting for RCPTs followed by DATA
+func (ss *Session) mailHandler(cmd string, arg string) {
+	switch cmd {
+	case "RCPT":
+		if (len(arg) < 4) || (strings.ToUpper(arg[0:3]) != "TO:") {
+			ss.send("501 Was expecting RCPT arg syntax of TO:<address>")
+			ss.logWarn("Bad RCPT argument: %q", arg)
+			return
+		}
+		// This trim is probably too forgiving
+		recip := strings.Trim(arg[3:], "<> ")
+		if _, _, err := stringutil.ParseEmailAddress(recip); err != nil {
+			ss.send("501 Bad recipient address syntax")
+			ss.logWarn("Bad address as RCPT arg: %q, %s", recip, err)
+			return
+		}
+		if ss.recipients.Len() >= ss.server.maxRecips {
+			ss.logWarn("Maximum limit of %v recipients reached", ss.server.maxRecips)
+			ss.send(fmt.Sprintf("552 Maximum limit of %v recipients reached", ss.server.maxRecips))
+			return
+		}
+		ss.recipients.PushBack(recip)
+		ss.logInfo("Recipient: %v", recip)
+		ss.send(fmt.Sprintf("250 I'll make sure <%v> gets this", recip))
+		return
+	case "DATA":
+		if arg != "" {
+			ss.send("501 DATA command should not have any arguments")
+			ss.logWarn("Got unexpected args on DATA: %q", arg)
+			return
+		}
+		if ss.recipients.Len() > 0 {
+			// We have recipients, go to accept data
+			ss.enterState(DATA)
+			return
+		}
+		// DATA out of sequence
+		ss.ooSeq(cmd)
+		return
+	}
+	ss.ooSeq(cmd)
+}
+
+// DATA
+func (ss *Session) dataHandler() {
+	recipients := make([]recipientDetails, 0, ss.recipients.Len())
+	// Get a Mailbox and a new Message for each recipient
+	msgSize := 0
+	if ss.server.storeMessages {
+		for e := ss.recipients.Front(); e != nil; e = e.Next() {
+			recip := e.Value.(string)
+			local, domain, err := stringutil.ParseEmailAddress(recip)
+			if err != nil {
+				ss.logError("Failed to parse address for %q", recip)
+				ss.send(fmt.Sprintf("451 Failed to open mailbox for %v", recip))
+				ss.reset()
+				return
+			}
+			if strings.ToLower(domain) != ss.server.domainNoStore {
+				// Not our "no store" domain, so store the message
+				mb, err := ss.server.dataStore.MailboxFor(local)
+				if err != nil {
+					ss.logError("Failed to open mailbox for %q: %s", local, err)
+					ss.send(fmt.Sprintf("451 Failed to open mailbox for %v", local))
+					ss.reset()
+					return
+				}
+				recipients = append(recipients, recipientDetails{recip, local, domain, mb})
+			} else {
+				log.Tracef("Not storing message for %q", recip)
+			}
+		}
+	}
+
+	ss.send("354 Start mail input; end with <CRLF>.<CRLF>")
+	var lineBuf bytes.Buffer
+	msgBuf := make([][]byte, 0, 1024)
+	for {
+		lineBuf.Reset()
+		err := ss.readByteLine(&lineBuf)
+		if err != nil {
+			if netErr, ok := err.(net.Error); ok {
+				if netErr.Timeout() {
+					ss.send("221 Idle timeout, bye bye")
+				}
+			}
+			ss.logWarn("Error: %v while reading", err)
+			ss.enterState(QUIT)
+			return
+		}
+		line := lineBuf.Bytes()
+		// ss.logTrace("DATA: %q", line)
+		if string(line) == ".\r\n" || string(line) == ".\n" {
+			// Mail data complete
+			if ss.server.storeMessages {
+				// Create a message for each valid recipient
+				for _, r := range recipients {
+					// TODO temporary hack to fix #77 until datastore revamp
+					mu, err := ss.server.dataStore.LockFor(r.localPart)
+					if err != nil {
+						ss.logError("Failed to get lock for %q: %s", r.localPart, err)
+						// Delivery failure
+						ss.send(fmt.Sprintf("451 Failed to store message for %v", r.localPart))
+						ss.reset()
+						return
+					}
+					mu.Lock()
+					ok := ss.deliverMessage(r, msgBuf)
+					mu.Unlock()
+					if ok {
+						expReceivedTotal.Add(1)
+					} else {
+						// Delivery failure
+						ss.send(fmt.Sprintf("451 Failed to store message for %v", r.localPart))
+						ss.reset()
+						return
+					}
+				}
+			} else {
+				expReceivedTotal.Add(1)
+			}
+			ss.send("250 Mail accepted for delivery")
+			ss.logInfo("Message size %v bytes", msgSize)
+			ss.reset()
+			return
+		}
+		// SMTP RFC says remove leading periods from input
+		if len(line) > 0 && line[0] == '.' {
+			line = line[1:]
+		}
+		// Second append copies line/lineBuf so we can reuse it
+		msgBuf = append(msgBuf, append([]byte{}, line...))
+		msgSize += len(line)
+		if msgSize > ss.server.maxMessageBytes {
+			// Max message size exceeded
+			ss.send("552 Maximum message size exceeded")
+			ss.logWarn("Max message size exceeded while in DATA")
+			ss.reset()
+			// Should really cleanup the crap on filesystem (after issue #23)
+			return
+		}
+	} // end for
+}
+
+// deliverMessage creates and populates a new Message for the specified recipient
+func (ss *Session) deliverMessage(r recipientDetails, msgBuf [][]byte) (ok bool) {
+	msg, err := r.mailbox.NewMessage()
+	if err != nil {
+		ss.logError("Failed to create message for %q: %s", r.localPart, err)
+		return false
+	}
+
+	// Generate Received header
+	stamp := time.Now().Format(timeStampFormat)
+	recd := fmt.Sprintf("Received: from %s ([%s]) by %s\r\n  for <%s>; %s\r\n",
+		ss.remoteDomain, ss.remoteHost, ss.server.domain, r.address, stamp)
+	if err := msg.Append([]byte(recd)); err != nil {
+		ss.logError("Failed to write received header for %q: %s", r.localPart, err)
+		return false
+	}
+
+	// Append lines from msgBuf
+	for _, line := range msgBuf {
+		if err := msg.Append(line); err != nil {
+			ss.logError("Failed to append to mailbox %v: %v", r.mailbox, err)
+			// Should really cleanup the crap on filesystem
+			return false
+		}
+	}
+	if err := msg.Close(); err != nil {
+		ss.logError("Error while closing message for %v: %v", r.mailbox, err)
+		return false
+	}
+
+	// Broadcast message information
+	broadcast := msghub.Message{
+		Mailbox: r.mailbox.Name(),
+		ID:      msg.ID(),
+		From:    msg.From(),
+		To:      msg.To(),
+		Subject: msg.Subject(),
+		Date:    msg.Date(),
+		Size:    msg.Size(),
+	}
+	ss.server.msgHub.Dispatch(broadcast)
+
+	return true
+}
+
+func (ss *Session) enterState(state State) {
+	ss.state = state
+	ss.logTrace("Entering state %v", state)
+}
+
+func (ss *Session) greet() {
+	ss.send(fmt.Sprintf("220 %v Inbucket SMTP ready", ss.server.domain))
+}
+
+// Calculate the next read or write deadline based on maxIdleSeconds
+func (ss *Session) nextDeadline() time.Time {
+	return time.Now().Add(time.Duration(ss.server.maxIdleSeconds) * time.Second)
+}
+
+// Send requested message, store errors in Session.sendError
+func (ss *Session) send(msg string) {
+	if err := ss.conn.SetWriteDeadline(ss.nextDeadline()); err != nil {
+		ss.sendError = err
+		return
+	}
+	if _, err := fmt.Fprint(ss.conn, msg+"\r\n"); err != nil {
+		ss.sendError = err
+		ss.logWarn("Failed to send: %q", msg)
+		return
+	}
+	ss.logTrace(">> %v >>", msg)
+}
+
+// readByteLine reads a line of input into the provided buffer. Does
+// not reset the Buffer - please do so prior to calling.
+func (ss *Session) readByteLine(buf io.Writer) error {
+	if err := ss.conn.SetReadDeadline(ss.nextDeadline()); err != nil {
+		return err
+	}
+	line, err := ss.reader.ReadBytes('\n')
+	if err != nil {
+		return err
+	}
+	_, err = buf.Write(line)
+	return err
+}
+
+// Reads a line of input
+func (ss *Session) readLine() (line string, err error) {
+	if err = ss.conn.SetReadDeadline(ss.nextDeadline()); err != nil {
+		return "", err
+	}
+	line, err = ss.reader.ReadString('\n')
+	if err != nil {
+		return "", err
+	}
+	ss.logTrace("<< %v <<", strings.TrimRight(line, "\r\n"))
+	return line, nil
+}
+
+func (ss *Session) parseCmd(line string) (cmd string, arg string, ok bool) {
+	line = strings.TrimRight(line, "\r\n")
+	l := len(line)
+	switch {
+	case l == 0:
+		return "", "", true
+	case l < 4:
+		ss.logWarn("Command too short: %q", line)
+		return "", "", false
+	case l == 4:
+		return strings.ToUpper(line), "", true
+	case l == 5:
+		// Too long to be only command, too short to have args
+		ss.logWarn("Mangled command: %q", line)
+		return "", "", false
+	}
+	// If we made it here, command is long enough to have args
+	if line[4] != ' ' {
+		// There wasn't a space after the command?
+		ss.logWarn("Mangled command: %q", line)
+		return "", "", false
+	}
+	// I'm not sure if we should trim the args or not, but we will for now
+	return strings.ToUpper(line[0:4]), strings.Trim(line[5:], " "), true
+}
+
+// parseArgs takes the arguments proceeding a command and files them
+// into a map[string]string after uppercasing each key.  Sample arg
+// string:
+//		" BODY=8BITMIME SIZE=1024"
+// The leading space is mandatory.
+func (ss *Session) parseArgs(arg string) (args map[string]string, ok bool) {
+	args = make(map[string]string)
+	re := regexp.MustCompile(` (\w+)=(\w+)`)
+	pm := re.FindAllStringSubmatch(arg, -1)
+	if pm == nil {
+		ss.logWarn("Failed to parse arg string: %q")
+		return nil, false
+	}
+	for _, m := range pm {
+		args[strings.ToUpper(m[1])] = m[2]
+	}
+	ss.logTrace("ESMTP params: %v", args)
+	return args, true
+}
+
+func (ss *Session) reset() {
+	ss.enterState(READY)
+	ss.from = ""
+	ss.recipients = nil
+}
+
+func (ss *Session) ooSeq(cmd string) {
+	ss.send(fmt.Sprintf("503 Command %v is out of sequence", cmd))
+	ss.logWarn("Wasn't expecting %v here", cmd)
+}
+
+// Session specific logging methods
+func (ss *Session) logTrace(msg string, args ...interface{}) {
+	log.Tracef("SMTP[%v]<%v> %v", ss.remoteHost, ss.id, fmt.Sprintf(msg, args...))
+}
+
+func (ss *Session) logInfo(msg string, args ...interface{}) {
+	log.Infof("SMTP[%v]<%v> %v", ss.remoteHost, ss.id, fmt.Sprintf(msg, args...))
+}
+
+func (ss *Session) logWarn(msg string, args ...interface{}) {
+	// Update metrics
+	expWarnsTotal.Add(1)
+	log.Warnf("SMTP[%v]<%v> %v", ss.remoteHost, ss.id, fmt.Sprintf(msg, args...))
+}
+
+func (ss *Session) logError(msg string, args ...interface{}) {
+	// Update metrics
+	expErrorsTotal.Add(1)
+	log.Errorf("SMTP[%v]<%v> %v", ss.remoteHost, ss.id, fmt.Sprintf(msg, args...))
+}
--- a/pkg/server/smtp/handler_test.go
+++ b/pkg/server/smtp/handler_test.go
@@ -0,0 +1,409 @@
+package smtp
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+
+	"log"
+	"net"
+	"net/textproto"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/jhillyerd/inbucket/pkg/config"
+	"github.com/jhillyerd/inbucket/pkg/msghub"
+	"github.com/jhillyerd/inbucket/pkg/storage"
+)
+
+type scriptStep struct {
+	send   string
+	expect int
+}
+
+// Test commands in GREET state
+func TestGreetState(t *testing.T) {
+	// Setup mock objects
+	mds := &datastore.MockDataStore{}
+
+	server, logbuf, teardown := setupSMTPServer(mds)
+	defer teardown()
+
+	// Test out some mangled HELOs
+	script := []scriptStep{
+		{"HELO", 501},
+		{"EHLO", 501},
+		{"HELLO", 500},
+		{"HELL", 500},
+		{"hello", 500},
+		{"Outlook", 500},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Valid HELOs
+	if err := playSession(t, server, []scriptStep{{"HELO mydomain", 250}}); err != nil {
+		t.Error(err)
+	}
+	if err := playSession(t, server, []scriptStep{{"HELO mydom.com", 250}}); err != nil {
+		t.Error(err)
+	}
+	if err := playSession(t, server, []scriptStep{{"HelO mydom.com", 250}}); err != nil {
+		t.Error(err)
+	}
+	if err := playSession(t, server, []scriptStep{{"helo 127.0.0.1", 250}}); err != nil {
+		t.Error(err)
+	}
+
+	// Valid EHLOs
+	if err := playSession(t, server, []scriptStep{{"EHLO mydomain", 250}}); err != nil {
+		t.Error(err)
+	}
+	if err := playSession(t, server, []scriptStep{{"EHLO mydom.com", 250}}); err != nil {
+		t.Error(err)
+	}
+	if err := playSession(t, server, []scriptStep{{"EhlO mydom.com", 250}}); err != nil {
+		t.Error(err)
+	}
+	if err := playSession(t, server, []scriptStep{{"ehlo 127.0.0.1", 250}}); err != nil {
+		t.Error(err)
+	}
+
+	if t.Failed() {
+		// Wait for handler to finish logging
+		time.Sleep(2 * time.Second)
+		// Dump buffered log data if there was a failure
+		_, _ = io.Copy(os.Stderr, logbuf)
+	}
+}
+
+// Test commands in READY state
+func TestReadyState(t *testing.T) {
+	// Setup mock objects
+	mds := &datastore.MockDataStore{}
+
+	server, logbuf, teardown := setupSMTPServer(mds)
+	defer teardown()
+
+	// Test out some mangled READY commands
+	script := []scriptStep{
+		{"HELO localhost", 250},
+		{"FOOB", 500},
+		{"HELO", 503},
+		{"DATA", 503},
+		{"MAIL", 501},
+		{"MAIL FROM john@gmail.com", 501},
+		{"MAIL FROM:john@gmail.com", 501},
+		{"MAIL FROM:<john@gmail.com> SIZE=147KB", 501},
+		{"MAIL FROM: <john@gmail.com> SIZE147", 501},
+		{"MAIL FROM:<first@last@gmail.com>", 501},
+		{"MAIL FROM:<first last@gmail.com>", 501},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Test out some valid MAIL commands
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM: <john@gmail.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM: <john@gmail.com> BODY=8BITMIME", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<john@gmail.com> SIZE=1024", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<host!host!user/data@foo.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<\"first last\"@space.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<user\\@internal@external.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<user\\>name@host.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<\"user>name\"@host.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<\"user@internal\"@external.com>", 250},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	if t.Failed() {
+		// Wait for handler to finish logging
+		time.Sleep(2 * time.Second)
+		// Dump buffered log data if there was a failure
+		_, _ = io.Copy(os.Stderr, logbuf)
+	}
+}
+
+// Test commands in MAIL state
+func TestMailState(t *testing.T) {
+	// Setup mock objects
+	mds := &datastore.MockDataStore{}
+	mb1 := &datastore.MockMailbox{}
+	msg1 := &datastore.MockMessage{}
+	mds.On("MailboxFor", "u1").Return(mb1, nil)
+	mb1.On("NewMessage").Return(msg1, nil)
+	mb1.On("Name").Return("u1")
+	msg1.On("ID").Return("")
+	msg1.On("From").Return("")
+	msg1.On("To").Return(make([]string, 0))
+	msg1.On("Date").Return(time.Time{})
+	msg1.On("Subject").Return("")
+	msg1.On("Size").Return(0)
+	msg1.On("Close").Return(nil)
+
+	server, logbuf, teardown := setupSMTPServer(mds)
+	defer teardown()
+
+	// Test out some mangled READY commands
+	script := []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"FOOB", 500},
+		{"HELO", 503},
+		{"DATA", 503},
+		{"MAIL", 503},
+		{"RCPT", 501},
+		{"RCPT TO", 501},
+		{"RCPT TO james@gmail.com", 501},
+		{"RCPT TO:<first last@host.com>", 501},
+		{"RCPT TO:<fred@fish@host.com", 501},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Test out some good RCPT commands
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<u1@gmail.com>", 250},
+		{"RCPT TO: <u2@gmail.com>", 250},
+		{"RCPT TO:u3@gmail.com", 250},
+		{"RCPT TO: u4@gmail.com", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<user\\@internal@external.com", 250},
+		{"RCPT TO:<\"first last\"@host.com", 250},
+		{"RCPT TO:<user\\>name@host.com>", 250},
+		{"RCPT TO:<\"user>name\"@host.com>", 250},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Test out recipient limit
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<u1@gmail.com>", 250},
+		{"RCPT TO:<u2@gmail.com>", 250},
+		{"RCPT TO:<u3@gmail.com>", 250},
+		{"RCPT TO:<u4@gmail.com>", 250},
+		{"RCPT TO:<u5@gmail.com>", 250},
+		{"RCPT TO:<u6@gmail.com>", 552},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Test DATA
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<u1@gmail.com>", 250},
+		{"DATA", 354},
+		{".", 250},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Test RSET
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<u1@gmail.com>", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	// Test QUIT
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<u1@gmail.com>", 250},
+		{"QUIT", 221},
+	}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	if t.Failed() {
+		// Wait for handler to finish logging
+		time.Sleep(2 * time.Second)
+		// Dump buffered log data if there was a failure
+		_, _ = io.Copy(os.Stderr, logbuf)
+	}
+}
+
+// Test commands in DATA state
+func TestDataState(t *testing.T) {
+	// Setup mock objects
+	mds := &datastore.MockDataStore{}
+	mb1 := &datastore.MockMailbox{}
+	msg1 := &datastore.MockMessage{}
+	mds.On("MailboxFor", "u1").Return(mb1, nil)
+	mb1.On("NewMessage").Return(msg1, nil)
+	mb1.On("Name").Return("u1")
+	msg1.On("ID").Return("")
+	msg1.On("From").Return("")
+	msg1.On("To").Return(make([]string, 0))
+	msg1.On("Date").Return(time.Time{})
+	msg1.On("Subject").Return("")
+	msg1.On("Size").Return(0)
+	msg1.On("Close").Return(nil)
+
+	server, logbuf, teardown := setupSMTPServer(mds)
+	defer teardown()
+
+	var script []scriptStep
+	pipe := setupSMTPSession(server)
+	c := textproto.NewConn(pipe)
+
+	// Get us into DATA state
+	if code, _, err := c.ReadCodeLine(220); err != nil {
+		t.Errorf("Expected a 220 greeting, got %v", code)
+	}
+	script = []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<u1@gmail.com>", 250},
+		{"DATA", 354},
+	}
+	if err := playScriptAgainst(t, c, script); err != nil {
+		t.Error(err)
+	}
+	// Send a message
+	body := `To: u1@gmail.com
+From: john@gmail.com
+Subject: test
+
+Hi!
+`
+	dw := c.DotWriter()
+	_, _ = io.WriteString(dw, body)
+	_ = dw.Close()
+	if code, _, err := c.ReadCodeLine(250); err != nil {
+		t.Errorf("Expected a 250 greeting, got %v", code)
+	}
+
+	if t.Failed() {
+		// Wait for handler to finish logging
+		time.Sleep(2 * time.Second)
+		// Dump buffered log data if there was a failure
+		_, _ = io.Copy(os.Stderr, logbuf)
+	}
+}
+
+// playSession creates a new session, reads the greeting and then plays the script
+func playSession(t *testing.T, server *Server, script []scriptStep) error {
+	pipe := setupSMTPSession(server)
+	c := textproto.NewConn(pipe)
+
+	if code, _, err := c.ReadCodeLine(220); err != nil {
+		return fmt.Errorf("Expected a 220 greeting, got %v", code)
+	}
+
+	err := playScriptAgainst(t, c, script)
+
+	// Not all tests leave the session in a clean state, so the following two
+	// calls can fail
+	_, _ = c.Cmd("QUIT")
+	_, _, _ = c.ReadCodeLine(221)
+
+	return err
+}
+
+// playScriptAgainst an existing connection, does not handle server greeting
+func playScriptAgainst(t *testing.T, c *textproto.Conn, script []scriptStep) error {
+	for i, step := range script {
+		id, err := c.Cmd(step.send)
+		if err != nil {
+			return fmt.Errorf("Step %d, failed to send %q: %v", i, step.send, err)
+		}
+
+		c.StartResponse(id)
+		code, msg, err := c.ReadResponse(step.expect)
+		if err != nil {
+			err = fmt.Errorf("Step %d, sent %q, expected %v, got %v: %q",
+				i, step.send, step.expect, code, msg)
+		}
+		c.EndResponse(id)
+
+		if err != nil {
+			// Return after c.EndResponse so we don't hang the connection
+			return err
+		}
+	}
+	return nil
+}
+
+// net.Pipe does not implement deadlines
+type mockConn struct {
+	net.Conn
+}
+
+func (m *mockConn) SetDeadline(t time.Time) error      { return nil }
+func (m *mockConn) SetReadDeadline(t time.Time) error  { return nil }
+func (m *mockConn) SetWriteDeadline(t time.Time) error { return nil }
+
+func setupSMTPServer(ds datastore.DataStore) (s *Server, buf *bytes.Buffer, teardown func()) {
+	// Test Server Config
+	cfg := config.SMTPConfig{
+		IP4address:      net.IPv4(127, 0, 0, 1),
+		IP4port:         2500,
+		Domain:          "inbucket.local",
+		DomainNoStore:   "bitbucket.local",
+		MaxRecipients:   5,
+		MaxIdleSeconds:  5,
+		MaxMessageBytes: 5000,
+		StoreMessages:   true,
+	}
+
+	// Capture log output
+	buf = new(bytes.Buffer)
+	log.SetOutput(buf)
+
+	// Create a server, don't start it
+	shutdownChan := make(chan bool)
+	ctx, cancel := context.WithCancel(context.Background())
+	teardown = func() {
+		close(shutdownChan)
+		cancel()
+	}
+	s = NewServer(cfg, shutdownChan, ds, msghub.New(ctx, 100))
+	return s, buf, teardown
+}
+
+var sessionNum int
+
+func setupSMTPSession(server *Server) net.Conn {
+	// Pair of pipes to communicate
+	serverConn, clientConn := net.Pipe()
+	// Start the session
+	server.waitgroup.Add(1)
+	sessionNum++
+	go server.startSession(sessionNum, &mockConn{serverConn})
+
+	return clientConn
+}
--- a/pkg/server/smtp/listener.go
+++ b/pkg/server/smtp/listener.go
@@ -0,0 +1,199 @@
+package smtp
+
+import (
+	"container/list"
+	"context"
+	"expvar"
+	"fmt"
+	"net"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/jhillyerd/inbucket/pkg/config"
+	"github.com/jhillyerd/inbucket/pkg/log"
+	"github.com/jhillyerd/inbucket/pkg/msghub"
+	"github.com/jhillyerd/inbucket/pkg/storage"
+)
+
+func init() {
+	m := expvar.NewMap("smtp")
+	m.Set("ConnectsTotal", expConnectsTotal)
+	m.Set("ConnectsHist", expConnectsHist)
+	m.Set("ConnectsCurrent", expConnectsCurrent)
+	m.Set("ReceivedTotal", expReceivedTotal)
+	m.Set("ReceivedHist", expReceivedHist)
+	m.Set("ErrorsTotal", expErrorsTotal)
+	m.Set("ErrorsHist", expErrorsHist)
+	m.Set("WarnsTotal", expWarnsTotal)
+	m.Set("WarnsHist", expWarnsHist)
+
+	log.AddTickerFunc(func() {
+		expReceivedHist.Set(log.PushMetric(deliveredHist, expReceivedTotal))
+		expConnectsHist.Set(log.PushMetric(connectsHist, expConnectsTotal))
+		expErrorsHist.Set(log.PushMetric(errorsHist, expErrorsTotal))
+		expWarnsHist.Set(log.PushMetric(warnsHist, expWarnsTotal))
+	})
+}
+
+// Server holds the configuration and state of our SMTP server
+type Server struct {
+	// Configuration
+	host            string
+	domain          string
+	domainNoStore   string
+	maxRecips       int
+	maxIdleSeconds  int
+	maxMessageBytes int
+	storeMessages   bool
+
+	// Dependencies
+	dataStore        datastore.DataStore         // Mailbox/message store
+	globalShutdown   chan bool                   // Shuts down Inbucket
+	msgHub           *msghub.Hub                 // Pub/sub for message info
+	retentionScanner *datastore.RetentionScanner // Deletes expired messages
+
+	// State
+	listener  net.Listener    // Incoming network connections
+	waitgroup *sync.WaitGroup // Waitgroup tracks individual sessions
+}
+
+var (
+	// Raw stat collectors
+	expConnectsTotal   = new(expvar.Int)
+	expConnectsCurrent = new(expvar.Int)
+	expReceivedTotal   = new(expvar.Int)
+	expErrorsTotal     = new(expvar.Int)
+	expWarnsTotal      = new(expvar.Int)
+
+	// History of certain stats
+	deliveredHist = list.New()
+	connectsHist  = list.New()
+	errorsHist    = list.New()
+	warnsHist     = list.New()
+
+	// History rendered as comma delim string
+	expReceivedHist = new(expvar.String)
+	expConnectsHist = new(expvar.String)
+	expErrorsHist   = new(expvar.String)
+	expWarnsHist    = new(expvar.String)
+)
+
+// NewServer creates a new Server instance with the specificed config
+func NewServer(
+	cfg config.SMTPConfig,
+	globalShutdown chan bool,
+	ds datastore.DataStore,
+	msgHub *msghub.Hub) *Server {
+	return &Server{
+		host:             fmt.Sprintf("%v:%v", cfg.IP4address, cfg.IP4port),
+		domain:           cfg.Domain,
+		domainNoStore:    strings.ToLower(cfg.DomainNoStore),
+		maxRecips:        cfg.MaxRecipients,
+		maxIdleSeconds:   cfg.MaxIdleSeconds,
+		maxMessageBytes:  cfg.MaxMessageBytes,
+		storeMessages:    cfg.StoreMessages,
+		globalShutdown:   globalShutdown,
+		dataStore:        ds,
+		msgHub:           msgHub,
+		retentionScanner: datastore.NewRetentionScanner(ds, globalShutdown),
+		waitgroup:        new(sync.WaitGroup),
+	}
+}
+
+// Start the listener and handle incoming connections
+func (s *Server) Start(ctx context.Context) {
+	addr, err := net.ResolveTCPAddr("tcp4", s.host)
+	if err != nil {
+		log.Errorf("Failed to build tcp4 address: %v", err)
+		s.emergencyShutdown()
+		return
+	}
+
+	log.Infof("SMTP listening on TCP4 %v", addr)
+	s.listener, err = net.ListenTCP("tcp4", addr)
+	if err != nil {
+		log.Errorf("SMTP failed to start tcp4 listener: %v", err)
+		s.emergencyShutdown()
+		return
+	}
+
+	if !s.storeMessages {
+		log.Infof("Load test mode active, messages will not be stored")
+	} else if s.domainNoStore != "" {
+		log.Infof("Messages sent to domain '%v' will be discarded", s.domainNoStore)
+	}
+
+	// Start retention scanner
+	s.retentionScanner.Start()
+
+	// Listener go routine
+	go s.serve(ctx)
+
+	// Wait for shutdown
+	<-ctx.Done()
+	log.Tracef("SMTP shutdown requested, connections will be drained")
+
+	// Closing the listener will cause the serve() go routine to exit
+	if err := s.listener.Close(); err != nil {
+		log.Errorf("Failed to close SMTP listener: %v", err)
+	}
+}
+
+// serve is the listen/accept loop
+func (s *Server) serve(ctx context.Context) {
+	// Handle incoming connections
+	var tempDelay time.Duration
+	for sessionID := 1; ; sessionID++ {
+		if conn, err := s.listener.Accept(); err != nil {
+			// There was an error accepting the connection
+			if nerr, ok := err.(net.Error); ok && nerr.Temporary() {
+				// Temporary error, sleep for a bit and try again
+				if tempDelay == 0 {
+					tempDelay = 5 * time.Millisecond
+				} else {
+					tempDelay *= 2
+				}
+				if max := 1 * time.Second; tempDelay > max {
+					tempDelay = max
+				}
+				log.Errorf("SMTP accept error: %v; retrying in %v", err, tempDelay)
+				time.Sleep(tempDelay)
+				continue
+			} else {
+				// Permanent error
+				select {
+				case <-ctx.Done():
+					// SMTP is shutting down
+					return
+				default:
+					// Something went wrong
+					s.emergencyShutdown()
+					return
+				}
+			}
+		} else {
+			tempDelay = 0
+			expConnectsTotal.Add(1)
+			s.waitgroup.Add(1)
+			go s.startSession(sessionID, conn)
+		}
+	}
+}
+
+func (s *Server) emergencyShutdown() {
+	// Shutdown Inbucket
+	select {
+	case <-s.globalShutdown:
+	default:
+		close(s.globalShutdown)
+	}
+}
+
+// Drain causes the caller to block until all active SMTP sessions have finished
+func (s *Server) Drain() {
+	// Wait for sessions to close
+	s.waitgroup.Wait()
+	log.Tracef("SMTP connections have drained")
+	s.retentionScanner.Join()
+}