East of the Sun, West of the Moon

2005/9/23

Help me remember

Filed under: General — Erwin @ 7:47 pm

… to check back on CD Baby by November 10? I’ll explain later, thanks!

Email, what email

Filed under: Software — Erwin @ 6:00 pm

So yesterday, email seemed quiet. Too quiet, in fact.

It turns out the cable ISP has (apparently) decided that blocking my incoming port 25 (SMTP, a.k.a email server) is a good thing. I assume this was a global change but I haven’t verified that yet.

<…digging for documentation of this policy…>

Ah, found it. Unfortunately no timestamp of any sort on the page so I don’t know if it was updated recently or what. At least they aren’t doing anything undocumented, which always nice in its own right.

Anyway, this meant that I was now on the receiving end of such a block. Previously I had helped out a friend whose SMTP server had gotten blocked. The way around it is to simply tell the server to open a(n additional) port elsewhere and have a friendly server elsewhere that can receive email on port 25 and configure it to redirect your domain to the new port.

The friendly server runs Exim and my previous experience was with Sendmail, so I had some research to do.

To open an extra port on my side (with sendmail) was easy enough, two extra lines in the sendmail.mc file:

DAEMON_OPTIONS(`Name=MTA')dnl
DAEMON_OPTIONS(`Name=MTA255, Port=255')dnl

I needed the first line so the server would also still listen on the regular port, for local clients.

To reconfigure the Exim server, these changes were needed:

  • Add a new transport that works just like SMTP, but on a different port:
    my_smtp:
      driver = smtp
      service = 255
    
  • Insert a new route (order matters here, unlike with the transport):
    my_route:
      driver = domainlist
      transport = my_smtp
      route_list =    my.dom.ain real.smtp.server bydns; \
                    *.my.dom.ain real.smtp.server bydns
      self = send
    

    That last line is supposedly vital, but given that I got it to work the first time around with it, I wasn’t in the mood to test if it would also work without it.

  • Of course one also must ensure that the relevant domains are on the relay_domains list. 😉

After altering the DNS zone newly sent email is now slowly but surely beginning to work, but I have no idea if already sent email will be hanging around for 4-5 days while the various mail-servers try to send it to the old (port-25-blocked) server, or that they’ll realize the MX situation has changed and act on it.

Still pondering if I can do something about that, but at least I can move forward now. *mutter*

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