Can't send/recv AOL e-mails

RouterOS General
1

AOL says they do not have our mail server’s IP/subnet blocked. I’ve checked all my firewalls and I still can’t figure this out.

First, our network layout:
[ISP-GW:x.x.96.33]—[SWITCH “A”]—[MIKROTIK:x.x.96.36||x.x.20.1]—[SWITCH “B”]—[MAILSERVER:x.x.20.75]

So far, it appears that any system connected to switch “A” on the x.x.96.x subnet is able to telnet just fine to, e.g.: mailin-03.mx.aol.com port 25

Any system connected to switch “B” on the x.x.20.x subnet - behind a Mikrotik - gets a connection timed out when connecting to AOL’s MX servers (as bolded above).

Yes, it looks like AOL is load-balancing incoming mails, but I have tried connecting to a single IP (e.g.: 64.12.138.120 port 25) from systems behind (switch “B”) and outside (switch “A”) of this Mikrotik and I get the same results: Switch “A”: Works; Switch “B”: Timeout.

If I had a long ethernet cable, I’d plug my own workstation directly into switch “A” and test that out… but so far, AOL appears to be the only one we’re having issues with.

We recently started routing outbound e-mails from our main mail server, connected to switch “A” at x.x.96.38, to our spam-/virus-filtering mail server at x.x.20.75 on switch “B”, which is why we have started to notice this issue.

Any ideas? There’s just this one thread that I found. I’m running 2.9.40 on the Mikrotik pictured above, and no, changing the MSS did not help.

2

AOL have some strict mail relaying rules. Make sure you have a reverse/PTR record set on your mail servers IP and setup a SPF record if you haven’t already.

3

also your customer’s computer have to be with relayed ipaddr. with reverse record on some ns.

4

Yeah, it’s not the Mikrotik.
I tried srcnat’ing the mail server at x.x.20.75 to an available IP from the x.x.96.x subnet and without any other changes, the mail server connects to AOL’s MX server. I turn the srcnat off, and it goes back to timing out.

Needless to say, I’m talking with AOL again. :unamused: