Intermittent error when sending via SOGo: SMTP authentication failure even with active session
First of all, thank you to the Mailcow team and community for the amazing work on this project — we really appreciate the effort you all put into maintaining and improving it! 🙏
I’m experiencing an intermittent issue in my Mailcow environment: users can log into SOGo, browse folders, receive emails just fine, but when they try to send, sometimes they get “SMTP authentication failure”.
If they retry immediately, the message is sent successfully.
Observed symptoms
Failure happens randomly across different accounts.
In SOGo, error shown: authentication failure when sending.
In Postfix logs:
warning: servermail-sogo-mailcow-1.servermail_mailcow-network[172.22.1.248]: SASL plain authentication failed: (reason unavailable), sasl_username=user@domain
In Dovecot logs:
auth-worker: HTTP request failed with closed for user user@domain
auth: lua(user@domain): unknown user (SHA1 of given password: c110dc)
imap-login: Disconnected: Connection closed (auth failed, 1 attempts in 6 secs)
IMAP sessions continue working, so the issue seems to only affect SMTP auth at sending time via SOGo.
Problem is intermittent, not constant.
Rspamd logs show recurrent messages such as:
lua got error IO write error: Connection refused in http callback
ps. Using Traefik as reverse proxy in front of Mailcow and ipv6 is disabled.
Question
Has anyone faced this behavior before?
It looks like a momentary failure in the communication between Dovecot ↔ auth backend (Lua/PHP-FPM via nginx:8081), but I haven’t pinpointed the real bottleneck yet.