The LDAP domain filter matched every entry with a mail attribute, so
membership accounts with external addresses (e.g. @gmail.com) made
those domains local and outbound mail to them bounced with 550 5.1.1.
Restrict the filter to the Postfix Users group, like the user filter.
Pin docker-mailserver to 15.1.0: v17 renamed the LDAP_QUERY_FILTER_*
variables and chowns /var/mail to 5000:5000 at startup, which breaks
this LDAP uid-per-mailbox setup.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
