On 2026-06-06, Greg Wooledge wrote: > I keep thinking it's probably something in the networking code. I'm > reminded of TCP Window Scaling, which caused a bunch of problems when > it was newly introduced. Devices which were not properly configured > sometimes could not communicate properly with Linux systems that had > TCP Window Scaling enabled. (This was not a bug in Linux. It was a > common bug or misconfiguration in other systems.)
Yes it could also be a security patch enforcing a new control which fails. It could be apparmor denying access, etc. This is why I suggest to look in the system logs. Looking in inn2 logs and dovecot logs could be useful too.
