Configuring an ASA for O365 Hybrid email.

[Dorifitox]

Hello community!

I couldn't find a search function, so if this has already been answered in the past I am very sorry.

But I am trying to get my ASA to allow all traffic across a NAT'd connection, I've put an access rule of:

access-list OUTSIDE extended permit tcp any host ##.###.###.### eq smtp

But when I put it in I specified port 25 not smtp. I basically need to be able to telnet to this machine on port 25, so it has to be open to all traffic types.

Any idea on how I can force it to allow more than just SMTP traffic?

Your responses are much appreciated!

[Jouni Forss]

Hi,

Since you configure the ACL with the port TCP/25 the ASA will simply convert that port to the well known name of SMTP since that its main purpose. In an ACL however the rules matches ANY traffic coming with the destination port TCP/25. The ACL itself doesnt take into account what traffic you run through that port.

If you have SMTP/ESMTP inspection active on the ASA I would imagine it probably will not like traffic other than SMTP using port TCP/25 as destination. In that case you might have to disable that inspection.

Hope this helps

- Jouni