Exchange 2013 unable to send email.

After we changed ISP our exchange server was unable to sent emails to some recipients. The error message it get from other servers was "421 Refused. Your reverse DNS entry does not resolve.". The problem was that ISP does not wrote PTR records in their DNS servers. When DNS records was ok. Problem was still there.
Short investigation show that we had 2 IP adresses on routers WAN interface, and default IP was not the same as dns record points to. The solution is to add NAT rule on the router so that source IP of the exchage server was changed to correct IP.

Exchange 2013 how to change banner message

get connectors list:

Get-Receiveconnector

set connector banner:

Set-Receiveconnector "connector name" -Banner "220 mail.domain.com"

check banner:

Get-Receiveconnector "connector name" | fl

delete banner:

Set-Receiveconnector "connector name" -Banner $null