MTS blocks port 25

MTS (Manitoba Telecom Services) is one of the largest providers of both high-speed and dial-up internet access in Manitoba.

Unfortunately, if you use them, and try to send mail through a mail server other than their own, you might run into problems.

Now Gmail, Hotmail, and other web-based email users are fine. It’s those using Outlook, Thunderbird, Apple Mail, Eudora, etc who might be in trouble. Most mail sent through these programs is sent across port 25. In recent times, it’s started to become a common practice amongst large ISP’s to start blocking this port. Why? Well a lot of spam is sent across port 25, and blocking that port is the easiest solution that many ISP’s have come up with to reduce the chance that they’re customers are flooding the net with spam through their service.

So what are your options if you need to use a mail server other than MTS’s? Well here are a few:

  • Switch to another ISP. This is obviously a somewhat drastic measure, but if you’ve been having other issues with MTS, now might be the time for a change. Currently, SkyWeb does not block port 25. It might be worth asking other ISP’s whether or not they block port 25.
  • E-mail MTS and ask them to open the port. I really don’t know if they will, or how long it takes for them to do it, but I would suspect that if they have to choose between opening a port or losing a customer, they’d probably simply open the port for your account.
  • Use another port. Some mail servers allow connections on various ports. For example, the University of Manitoba has a nice writeup for students who connect through MTS but wish to use the Universities mail servers. They even include specific instructions for popular mail clients. You can read about it here (Web Archive). Alternately, if you’ve got your own website, you can contact your web host and ask if they have other ports available ( for example allows connections over both ports 25 and 26 – I was able to connect using TLS through port 26). You can also investigate the option of connecting through SSL. This typically uses a different port (commonly 587 or 465).