==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.2
- Linux/BSD distribution name and version: Ubuntu 14.04
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Nginx
- Manage mail accounts with iRedAdmin-Pro? Yes, v2.1.3 (MySQL)
====

Getting the following log entries occasionally from a user. I can't tell exactly why it's occurring. Is he being a bad boy, or just a problem with his PC. Thoughts?

Feb 10 08:38:25 iredmail postfix/smtpd[15370]: warning: hostname cust.138025.secret.hidden.net does not resolve to address 111.222.333.444: Name or service not known
Feb 10 08:38:25 iredmail postfix/smtpd[15370]: connect from unknown[111.222.333.444]
Feb 10 08:38:25 iredmail postfix/smtpd[15370]: E3E10325336: client=unknown[111.222.333.444], sasl_method=LOGIN, sasl_username=auser@mydomain.com
Feb 10 13:38:25 iredmail postfix/smtpd[15370]: fatal: watchdog timeout