So, I don’t think this is a Mailcow issue but wanted to check if I’m the only one seeing it: if I set my account’s outgoing account to use SSL/TLS over port 465, despite seeing the message marked as “delivered” in Postfix logs
2024-03-05T18:53:44+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:53:44 a2c3439d83b8 postfix/qmgr[378]: A21F358078D8: from=<xxxx@mydomain.xxx>, size=603, nrcpt=1 (queue active)
2024-03-05T18:53:44+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:53:44 a2c3439d83b8 postfix/smtp[829]: Trusted TLS connection established to gmail-smtp-in.l.google.com[173.194.73.26]:25: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-256)
2024-03-05T18:53:45+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:53:45 a2c3439d83b8 postfix/smtp[829]: A21F358078D8: to=<maddler@gmail.com>, relay=gmail-smtp-in.l.google.com[173.194.73.26]:25, delay=1.8, delays=0.99/0.02/0.31/0.5, dsn=2.0.0, status=sent (250 2.0.0 OK 1709664825 i12-20020a0565123e0c00b005134b31c12csi1007428lfv.298 - gsmtp)
2024-03-05T18:53:45+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:53:45 a2c3439d83b8 postfix/qmgr[378]: A21F358078D8: removed
It will not land into my Gmail mailbox. It works fine if I use STARTTLS.
Scratching my head…
And this is the log when sending with STARTTLS instead (and correctly delivered to mailbox)
2024-03-05T18:57:13+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:57:13 a2c3439d83b8 postfix/smtp[844]: Trusted TLS connection established to gmail-smtp-in.l.google.com[2a00:1450:400c:c0c::1a]:25: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-256)
2024-03-05T18:57:13+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:57:13 a2c3439d83b8 postfix/smtp[844]: 822AC5801EFA: to=<maddler@gmail.com>, relay=gmail-smtp-in.l.google.com[2a00:1450:400c:c0c::1a]:25, delay=1.2, delays=0.49/0.02/0.2/0.46, dsn=2.0.0, status=sent (250 2.0.0 OK 1709665033 o7-20020a05600c510700b00412eef1ebaasi759237wms.165 - gsmtp)
2024-03-05T18:57:13+00:00 localhost.localdomain docker/mailcowdockerized-postfix-mailcow-1[2787384]: Mar 5 18:57:13 a2c3439d83b8 postfix/qmgr[378]: 822AC5801EFA: removed
Definitely something happening something on Gmail, I’m also receiving the delivery report immediately, just the mail not showing in the mailbox.
The thing I spotted is that while sending over SSL/TLS connection goes to IPv6, rather than IPv4 while using STARTTLS.