Logger for OpenSMTPD failed authentication attempts using OpenSMTPD reporting API.
The logs can be processed with fail2ban to block hosts with excessive failed login attempts.
May 1 03:27:52 host smtpd[161]: auth-reporter: failed authentication from [email protected] address=1.2.3.4 host=host.domain.com
[Definition]
_daemon = smtpd
journalmatch = _SYSTEMD_UNIT=opensmtpd.service
failregex = ^.*: auth-reporter: failed authentication from user=.* address=<HOST> host=.*$