For some reason the postfix `main.cf` on one of our mail servers was missing the auth parts of the per-domain mail relaying changes !1389. We had per domain relayhost configuration, but relayauth was disabled. Updating to 3.3.0 fixed that issue: ```diff --- etc/postfix/main.cf 2025-04-28 01:45:21.000000000 +0200 +++ /etc/postfix/main.cf 2025-05-19 14:12:16.505958275 +0200 @@ -761,10 +761,10 @@ address_verify_negative_refresh_time = 60s enable_original_recipient = no sender_dependent_relayhost_maps = proxy:mysql:/etc/postfix/mysql-virtual_sender-relayhost.cf -smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd +smtp_sasl_password_maps = proxy:mysql:/etc/postfix/mysql-virtual_sender-relayauth.cf, texthash:/etc/postfix/sasl_passwd smtp_sender_dependent_authentication = yes -smtp_sasl_auth_enable = no -smtp_sasl_security_options = +smtp_sasl_auth_enable = yes +smtp_sasl_security_options = noanonymous, noplaintext smtp_sasl_tls_security_options = noanonymous authorized_flush_users = ``` However that introduced another issue: we were doing per-domain relaying without a username/password. This worked for the whole server (setting `relayhost`) and it worked before the update (because `smtp_sasl_auth_enable` used to be `no`) but it didn't work after the update: ``` server postfix/smtp[XXXXX]: XXXXXXXXXX: to=<user@external.com>, relay=relay.example.com[XXX.XXX.XXX.XXX]:25, delay=0.5, delays=0.23/0.02/0.26/0, dsn=4.7.0, status=deferred (SASL authentication failed; cannot authenticate to server relay.example.com[XXX.XXX.XXX.XXX]: no mechanism available) ``` That's because `/etc/postfix/mysql-virtual_sender-relayauth.cf` returns a non-null `user:pass` answer if there is any relaying configured, even if there isn't a username or password. I will submit a patch to fix this.