Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Port translation in router causing some email to fail

We are in the process of setting up a spam filter  (SAVASM). One change we are making is to push incoming email on port 25  through our spam filter/server but have users actually send their email  on a different port. I am attempting to make this happen by using port  address translation to send port 25 traffic to the SAVASM server IP.

As a step in making this change I setup port translation without  actually changing the IP addresses. The NAT rules for the email server  went from one Static NAT rule with no port specified, to multiple Static  NAT rules each with a port or group matching the Access Rules for that  server (smtp, pop3, http, https, and some other custom ports).

The problem we are running into is confusing. Some outgoing mail  through this server is failing when the router has the multiple NAT  rules with port translation settings. Email goes through fine FROM our  email to our internal accounts and to Gmail. However email fails when  FROM our client's email address TO our client's email or their personal  Comcast. The only situation that worked for them was if they changed  FROM to Comcast and then messages went through fine to both Comcast and  the client's accounts. Switching back to regular Static NAT rule  everything then worked for them.

Does anyone have a clue as to what might be going on? We are on a  Cisco ASA 5500 box. Thansk

Everyone's tags (2)
New Member

Re: Port translation in router causing some email to fail

Hmm, I think I have seen issues like this and the true problem was that when the server would go out, it would use the interface IP like a normal host instead of whatever IP address was on the PAT statement.

So like if you are patting with something like this

static (inside,outside) tcp 25 25

You sometimes need to add something like

nat (inside) 55

global (outside) 55

That way you appear as when you go out.

New Member

Re: Port translation in router causing some email to fail

I gave up getting port translation going and went with two unique IP addresses. Thanks anyway for your help.