From b7809d9c387c7338402d5e5a9ef2d3f74c7b80bc Mon Sep 17 00:00:00 2001
From: Sebastijan Zindl <sebastijan.zindl@proton.ch>
Date: Fri, 10 Jul 2026 12:42:38 +0200
Subject: [PATCH] fix(BRIDGE-582): empty address list return nil instead of
 empty list per RFC3501

---
 imap/envelope.go      |  2 +-
 imap/envelope_test.go | 29 +++++++++++++++++++++++++++++
 imap/params.go        |  4 ++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/imap/envelope.go b/imap/envelope.go
index df5a5afc..4085d1fd 100644
--- a/imap/envelope.go
+++ b/imap/envelope.go
@@ -80,7 +80,7 @@ func tryParseAddressList(val string) []*mail.Address {
 	addr, err := rfc5322.ParseAddressList(val)
 	if err != nil {
 		logrus.WithError(err).Error("Failed to parse address")
-		return []*mail.Address{{Name: val}}
+		return nil // RFC3501 empty address list should return NIL
 	}
 
 	return addr
diff --git a/imap/envelope_test.go b/imap/envelope_test.go
index d933be80..733990d4 100644
--- a/imap/envelope_test.go
+++ b/imap/envelope_test.go
@@ -24,3 +24,32 @@ func TestEnvelope(t *testing.T) {
 
 	assert.Equal(t, "(\"Sat, 03 Apr 2021 15:13:53 +0000\" \"this is currently a draft\" ((NIL NIL \"somebody\" \"pm.me\")) ((NIL NIL \"somebody\" \"pm.me\")) ((NIL NIL \"somebody\" \"pm.me\")) ((\"Somebody\" NIL \"somebody\" \"pm.me\")) NIL NIL NIL \"<X9xiWTZnfxfC0wGLBI9t-WEJCOSO_pT67TjlDDKZxzs7TFRCvzCF8lCtqrflZ9n2Z8Ve3rhwYE-vzUGkgOJWaZK4VWMk_WbertE5uklqS8A=@pm.me>\")", envelope)
 }
+
+func TestEnvelopeEmptyAddressList(t *testing.T) {
+	t.Parallel()
+
+	for name, tc := range map[string]struct {
+		msg      string
+		envelope string
+	}{
+		"empty To": {
+			msg:      "From: a@b.com\r\nTo:\r\nSubject: test\r\n\r\nbody",
+			envelope: `(NIL "test" ((NIL NIL "a" "b.com")) ((NIL NIL "a" "b.com")) ((NIL NIL "a" "b.com")) NIL NIL NIL NIL NIL)`,
+		},
+		"empty Cc": {
+			msg:      "From: a@b.com\r\nTo: x@y.com\r\nCc:\r\nSubject: test\r\n\r\nbody",
+			envelope: `(NIL "test" ((NIL NIL "a" "b.com")) ((NIL NIL "a" "b.com")) ((NIL NIL "a" "b.com")) ((NIL NIL "x" "y.com")) NIL NIL NIL NIL)`,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			header, err := rfc822.Parse([]byte(tc.msg)).ParseHeader()
+			require.NoError(t, err)
+
+			envelope, err := imap.Envelope(header)
+			require.NoError(t, err)
+			assert.Equal(t, tc.envelope, envelope)
+		})
+	}
+}
diff --git a/imap/params.go b/imap/params.go
index 57959d93..4dd1516f 100644
--- a/imap/params.go
+++ b/imap/params.go
@@ -130,6 +130,10 @@ func (c *paramList) addMap(writer parListWriter, v map[string]string) *paramList
 }
 
 func (c *paramList) addAddresses(writer parListWriter, v []*mail.Address) *paramList {
+	if len(v) == 0 {
+		return c.addString(writer, "")
+	}
+
 	c.onWrite(writer)
 
 	child := c.newChildList(writer)