Still Not Quite There with postfix & dovecot w/system & virtual users

I appreciate the help I got on an earlier post about this situation. While there were a lot of other things that were wrong with my configuration in addition to what users here pointed out, the suggestions were helpful for getting me to where I am. However, I'm still not there yet :). I am trying to configure postfix and dovecot 2.4.1 under Debian Trixie to handle both system and virtual users. Some of my virtual users have the same username part as system users (e.g., system account ‘mark’ and virtual user ‘mark@jumpforjoysoftware.com’). I’ve been struggling with getting help from Claude Code and Gemini Pro for several days now and still can’t get everything working. From watching the logs, the problem appears to stem from the username part not being extracted from the FQ user before authenticating against the system user database. Here are what I believe are the relevant sections of my dovecot.conf: auth_username_format = %{user | lower} # virtual users specified first so search will end when they are found passdb passwd-file { passwd_file_path = /etc/dovecot/passwd } userdb passwd-file { passwd_file_path = /etc/dovecot/passwd userdb_fields { uid = 5000 gid = 5000 home = /var/mail/vhosts/%{user | domain | lower }/%{user | username | lower } mail_driver = maildir mail_path = ~/Maildir } } # system users passdb pam { # apparently, this next line gets ignored auth_username_format = %{user | username | lower} service_name = dovecot } userdb passwd { # or maybe this line does auth_username_format = %{user | username | lower} userdb_fields { home = /home/%{user} mail_driver = maildir mail_path = ~/Maildir } } protocol lmtp { auth_username_format = %{user | username | lower} } service lmtp { unix_listener /var/spool/postfix/private/dovecot-lmtp { mode = 0660 user = postfix group = postfix } } # not sure this is part of the problem, but... service auth { unix_listener /var/spool/postfix/private/auth { mode = 0660 user = postfix group = postfix } } I believe the relevant sections of my postfix main.cf file are: My system hostname is theboilingfrog.net.myhostname = mail.theboilingfrog.net mydomain = theboilingfrog.net myorigin = $mydomain mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain mailbox_transport = lmtp:unix:private/dovecot-lmtp virtual_transport = lmtp:unix:private/dovecot-lmtp This configuration fails to recognize mark@theboilingfrog.net...which (mailto:mark@theboilingfrog.net...which) is why I think the passdb pam block is ignoring the auth_username_format directive which should strip out the username portion. Claude Code finally got around to suggesting I cut dovecot out of the loop for delivery of emails to system users. I guess I could do that, but I'd love to know if it's possible to keep dovecot engaged with delivering system user emails and have it work property. Another thing is I could update all my email clients to use 'mark' rather than 'mark@theboilingfrog.net' to access their email. But, again, I'm curious if there's a way to configure things so I don't have to do that. If it turns out what I'm trying to do is not supported, please let me know. - Mark