Email notifications silently failing with Postfix 3.7+

resolved Mattermost configuration Reported 2026-02-18 Verified 2026-03-02

TLS mismatch between Mattermost SMTP client and Postfix 3.7+ causes email notifications to fail without any error in the Mattermost logs.

Error Messages

TLS handshake failedconnection reset by peer

Resolutions (1)

high confidence 23 verified

Set smtpd_tls_mandatory_protocols in Postfix main.cf:

smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1

Then in Mattermost, set SMTP security to STARTTLS.

Verified by 23 users Added 2026-02-20

Applies to: 9.2, 9.3 on docker