Allow AUTH=<> FROM parameter (#284)

* Use backtick on regex
* Accept AUTH=<> FROM parameter
* Update changelog

CHANGELOG.md

@@ -6,6 +6,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Fixed
+- Support for `AUTH=<>` FROM parameter (#284)
+
+
 ## [v3.0.2] - 2022-07-04
 
 Note: We had to abandon the 3.0.1 release, see the blog post [What happened to

pkg/server/smtp/handler.go

@@ -54,11 +54,11 @@ const (
 	QUIT
 )
 
-// fromRegex captures the from address and optional BODY=8BITMIME clause.  Matches FROM, while
-// accepting '>' as quoted pair and in double quoted strings (?i) makes the regex case insensitive,
-// (?:) is non-grouping sub-match
+// fromRegex captures the from address and optional parameters.  Matches FROM, while accepting '>'
+// as quoted pair and in double quoted strings (?i) makes the regex case insensitive, (?:) is
+// non-grouping sub-match.  Accepts empty angle bracket value in options for 'AUTH=<>'.
 var fromRegex = regexp.MustCompile(
-	"(?i)^FROM:\\s*<((?:(?:\\\\>|[^>])+|\"[^\"]+\"@[^>])+)?>( [\\w= ]+)?$")
+	`(?i)^FROM:\s*<((?:(?:\\>|[^>])+|"[^"]+"@[^>])+)?>( [\w= ]+(?:=<>)?)?$`)
 
 func (s State) String() string {
 	switch s {

pkg/server/smtp/handler_test.go

@@ -193,6 +193,10 @@ func TestReadyState(t *testing.T) {
 		{"RSET", 250},
 		{"MAIL FROM:<john@gmail.com> SIZE=1024", 250},
 		{"RSET", 250},
+		{"MAIL FROM:<john@gmail.com> SIZE=1024 BODY=8BITMIME", 250},
+		{"RSET", 250},
+		{"MAIL FROM:<bounces@onmicrosoft.com> SIZE=4096 AUTH=<>", 250},
+		{"RSET", 250},
 		{"MAIL FROM:<host!host!user/data@foo.com>", 250},
 		{"RSET", 250},
 		{"MAIL FROM:<\"first last\"@space.com>", 250},