cannot send email: client QUITs after successful Authentication

[oljask]

Steps to reproduce

Click "SEND"

Expected behavior

Message sent

Actual behavior

2. "Could not send message" in red

Mail app version

5.5.8

Nextcloud version

32.0.0

Mailserver or service

Postfix 3.11

Operating system

FreeBSD 14.3

PHP engine version

PHP 8.3

Nextcloud memory caching

APCu

Web server

Nginx

Database

MariaDB

Additional info

Please advise on debugging mailapp. I can`t find related messages in nextcloud.log as it very message intensive.

Only related logging info i have is from postfix and it is very terse:

: unknown[xxxx:xxxx:xxxx:xx::x]: 235 2.7.0 Authentication successful
: smtp_stream_setup: maxtime=300 enable_deadline=0 min_data_rate=0
: watchdog_pat: 0x3f36a2010c90
: < unknown[xxxx:xxxx:xxxx:xx::x]: QUIT
: > unknown[xxxx:xxxx:xxxx:xx::x]: 221 2.0.0 Bye