I can not understand why there is a long connection to iredmail?

Question

Debian

Good afternoon.
The problem is this, there is a server on E3 16 GB of frame, debian and iredmail are installed. Everything is quite simple, but only if you start sending mail through it, then it does this for a very long time and it doesn’t matter through the client or directly through the web of the muzzle, it thinks, then everything is fine, the letter leaves and quickly reaches the addressee.
What could be the problem?
I thought about plugins, but they are mostly focused more on incoming mail. Maybe someone has come across this.

Answer 1

Most likely, dns is configured incorrectly somewhere or a non-existent host or non-existent dns address is registered.