diff --git a/pkg/message/manager.go b/pkg/message/manager.go
index fe9b650..6370ea6 100644
--- a/pkg/message/manager.go
+++ b/pkg/message/manager.go
@@ -112,7 +112,7 @@ func (s *StoreManager) GetMetadata(mailbox string) ([]*Metadata, error) {
 // GetMessage returns the specified message.
 func (s *StoreManager) GetMessage(mailbox, id string) (*Message, error) {
 	sm, err := s.Store.GetMessage(mailbox, id)
-	if err != nil {
+	if err != nil || sm == nil {
 		return nil, err
 	}
 	r, err := sm.Source()
@@ -148,7 +148,7 @@ func (s *StoreManager) RemoveMessage(mailbox, id string) error {
 // SourceReader allows the stored message source to be read.
 func (s *StoreManager) SourceReader(mailbox, id string) (io.ReadCloser, error) {
 	sm, err := s.Store.GetMessage(mailbox, id)
-	if err != nil {
+	if err != nil || sm == nil {
 		return nil, err
 	}
 	return sm.Source()
diff --git a/pkg/rest/apiv1_controller.go b/pkg/rest/apiv1_controller.go
index ea71e43..d9795eb 100644
--- a/pkg/rest/apiv1_controller.go
+++ b/pkg/rest/apiv1_controller.go
@@ -53,14 +53,13 @@ func MailboxShowV1(w http.ResponseWriter, req *http.Request, ctx *web.Context) (
 		return err
 	}
 	msg, err := ctx.Manager.GetMessage(name, id)
-	if err == storage.ErrNotExist {
+	if err != nil && err != storage.ErrNotExist {
+		return fmt.Errorf("GetMessage(%q) failed: %v", id, err)
+	}
+	if msg == nil {
 		http.NotFound(w, req)
 		return nil
 	}
-	if err != nil {
-		// This doesn't indicate empty, likely an IO error
-		return fmt.Errorf("GetMessage(%q) failed: %v", id, err)
-	}
 	attachParts := msg.Attachments()
 	attachments := make([]*model.JSONMessageAttachmentV1, len(attachParts))
 	for i, part := range attachParts {
@@ -146,14 +145,13 @@ func MailboxSourceV1(w http.ResponseWriter, req *http.Request, ctx *web.Context)
 		return err
 	}
 	r, err := ctx.Manager.SourceReader(name, id)
-	if err == storage.ErrNotExist {
+	if err != nil && err != storage.ErrNotExist {
+		return fmt.Errorf("SourceReader(%q) failed: %v", id, err)
+	}
+	if r == nil {
 		http.NotFound(w, req)
 		return nil
 	}
-	if err != nil {
-		// This doesn't indicate missing, likely an IO error
-		return fmt.Errorf("SourceReader(%q) failed: %v", id, err)
-	}
 	// Output message source
 	w.Header().Set("Content-Type", "text/plain")
 	_, err = io.Copy(w, r)
diff --git a/pkg/storage/mem/store.go b/pkg/storage/mem/store.go
index 16b094e..47ef265 100644
--- a/pkg/storage/mem/store.go
+++ b/pkg/storage/mem/store.go
@@ -93,7 +93,11 @@ func (s *Store) AddMessage(message storage.Message) (id string, err error) {
 // GetMessage gets a mesage.
 func (s *Store) GetMessage(mailbox, id string) (m storage.Message, err error) {
 	s.withMailbox(mailbox, false, func(mb *mbox) {
-		m = mb.messages[id]
+		var ok bool
+		m, ok = mb.messages[id]
+		if !ok {
+			m = nil
+		}
 	})
 	return m, err
 }