Comment 7 for bug 1753470

Do you have mail in the queue? -> sudo mailq

Do you have another 5min cron job that is perhaps failing and therefore sending an email?

Can you see any ownership and permissions problems in the postfix directories? Try "sudo postfix check", and maybe do a quick manual inspection in /var/spool, /var/lib, /var/mail directories

Do you have users and groups coming from a network source, like ldap, nis, ad, and maybe the postfix user or group is mixed with that?

Can you try running that postconf command as the postfix user, or as root if your previous attempt was as postfix or a regular user? Something like "sudo -u postfix -H postconf -h queue_directory"

Thanks