I would test Kolab4 with k3s setup but it fails because amavis-container in postfix-pod won't start.
In my logfiles i found this:

2025-01-04T08:46:57.445404536+01:00 stderr F <5>Found secondary av scanner ClamAV-clamscan at /usr/bin/clamscan
2025-01-04T08:46:57.445498999+01:00 stderr F <6>Deleting db files nanny.db,db.002,db.001,__db.003,snmp.db in /var/spool/amavisd/db
2025-01-04T08:46:57.446392015+01:00 stderr F <6>Creating db in /var/spool/amavisd/db/; BerkeleyDB 0.64, libdb 5.3
2025-01-04T08:46:57.464079589+01:00 stderr F <6>initializing Mail::SpamAssassin (0)
2025-01-04T08:46:57.464093562+01:00 stderr F <6>SpamAssassin debug facilities: info
2025-01-04T08:46:57.465800373+01:00 stderr F <3>(!!)TROUBLE in pre_loop_hook: config: no rules were found! Do you need to run 'sa-update'?
2025-01-04T08:46:57.465810536+01:00 stderr F <6>sd_notify (no socket): STOPPING=1\nSTATUS=TROUBLE in pre_loop_hook: config: no rules were found! Do you need to run 'sa-update'?
2025-01-04T08:46:57.466285114+01:00 stderr F Suicide () TROUBLE in pre_loop_hook: config: no rules were found! Do you need to run 'sa-update'?
2025-01-04T08:46:57.466292375+01:00 stderr F Compilation failed in require at /usr/sbin/amavisd line 103.
2025-01-04T08:46:57.466294664+01:00 stderr F BEGIN failed--compilation aborted at /usr/sbin/amavisd line 103.

it looks like a problem with spamassasin