==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.99
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Centos
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? 3.7
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

We have an internal system which sends an e-mail message to multiple internal accounts hosted by iRedMail several times a day.   The frequency  of these messages and the number of accounts sent to varies.   It can be a few hundred accounts.

We're finding almost everytime this process runs it gets bounces which state "unknown user account" for sometimes as many as 20 or 25% of the recipients.   These accounts do exist.   Sending a message to any of the "unknown user account" accounts through SOGo works fine.

In checking the logs I've found several lines similar to the following:
Jun 25 23:11:23 stmail fail2ban.filter[6746]: INFO [postfix-iredmail] Ignore 10.3.1.4 by ip

The ip 10.3.1.4 is the IP of the system which sends the messages to our internal iredmail server.

I've modified fail2ban to exclude this address by changing the file /etc/fail2ban/jail.conf and modifying the ignoreip setting to:
ignoreip = 127.0.0.1/8 10.3.1.4/16

I have restarted the service.

Would fail2ban generate an "Unknown user account" bounce?   It seems like it prevent the connection instead of sending a bounce.   

Has anyone seen a problem like this?

Thanks,
Bob