Note: Telia is the name of a large internet service provider in Sweden
When I moved recently, my self-hosted email server stopped working. Quick troubleshooting showed that no traffic could neither be sent nor received on port 25, the port used for email. I searched for information about the problem on the internet and found Flashback and SweClockers threads informing me that this was Telia's doing: They block all traffic on port 25 and some additional ports in their network. In my opinion, this is a very serious restriction of online freedom and a blow to democracy and privacy. Communication must be allowed without big brother watching.
In the same forum threads I was also informed that it is not uncommon for ISPs to block port 25, but that there also are ones with sense to leave it open. However, I am locked to Telia through my landlord, otherwise I would have switched to another provider as soon as possible. E-mail is one of the few remaining widespread decentralized communication standards on the internet. By blocking port 25, people are being forced to use services like Gmail or Outlook with all the privacy violations that entails (Google or Microsoft will be able to read all your emails). Telia provides an SMTP relay that can forward emails from within Telia's network, but that only lets Telia read my email instead. I liken this to a city banning the publication of all newspapers except those reviewed and censored by the city management. Sure, you can still communicate on other ports (though not with regular e-mail, you have to switch to another medium), and with VPS and VPN you can bypass Telia's firewall, but it's bad enough to significantly complicate private communication.
ISPs who block port 25 usually justify this restriction by saying that they thereby prevent spam. This has never been an acceptable acceptable argument as you should not collectively punish entire societies for crimes committed by individuals. But especially today, when we have SPF that can verify that an email comes from an authorized domain, it is unacceptable to continue to block port 25. I therefore hope that Telia and other ISPs continuously evaluate their firewall policies and properly justify why they choose to block certain ports. Telia does not justify its policy at all. They don't document it either. Only a single small line of text on the whole of telia.se contains the following:
The following ports are blocked in Telia's network: 135-139, 445, 25, 53.
When I call Telia's customer service, however, they know nothing about blocked ports and find nothing in their internal documentation, despite persistent searching. The only documentation about Telia's SMTP relay I can find also comes from various internet forums.
I hope that Telia and other ISPs will lift this firewall which today cannot be motivated by other than dishonest reasons. The fact that it is possible to communicate on other ports is not enough: You should not be allowed to shut down all newspapers for the reason that there are people who send out unwanted ad leaflets and say that this does not prevent the spread of socially important information as it is still permitted to go door-to-door. SPF prevents spam better than an ip-blacklist. Can you even say that a household has broadband if it can't send and receive e-mail, a basic function of a free internet? Everyone who can should move from Telia and other broadband providers that block important ports, for the sake of democracy and the free internet.