Running a mail server under TDC
Stupidly, I got into the habit many years ago of running my own server for dlade.net. This is always an extra cause of stress when moving anywhere, since it means I have to take down my primary mail server and not be quite sure when and how I will be able to get it back up again. And moving is often the time when I need email the most.
Having moved a few times (I lived in six places during my six years in London, moving more than once a year in the beginning), I was quite prepared for it this time, and even read about how to run a mail server in the TDC FAQ. When I finally got to set it all up, however, nothing worked the way I expected it to, and I could neither receive nor send email from my server, because port 25 was blocked both ways.
Reading the FAQ again, I found new information that mentioned that port 25 is blocked and you need to route your email via the server asmtp.mail.dk (with authentication) on the way out and the server backup-mx.post.tele.dk on the way in. However, neither of these would actually accept email for my domain, so I gave up for a short while. Googling randomly on the matter a bit later turned up the unauthenticated server smtp.mail.dk for sending email, which wasn’t mentioned anywhere in the FAQ, and finally four days after the move I could start sending email by myself. Incoming mail still had to go via my secondary mail server and fetchmail from there.
Today, as I was preparing to write this, as a way of spreading the knowledge of smtp.mail.dk a bit more (since it was hardly mentioned anywhere that I could find), I was again looking through the FAQ and today found a new entry that claims that port 25 should be open if you have a fixed IP address, and that you can ask for it to be opened if it isn’t already. So I called customer service, who impressively answered straight away and understood what I was talking about, and a few minutes and an automatic cable modem restart later, my mail server is now accessible from the rest of the world.
