Another T-2 customer here. I never ran into issues with port blocking (but didn't try 25/53), even more, I had a "free" static IPv4 on DSL before we got the fiber line, but I've lately been noticing random connection slowdowns. Never had significant slowdowns with DSL.

I've talked to a few people (Telemach customers) who told me it happens every now and then, they call the support center that tells them to restart the modem (even if they'd done it before) and then the connection magically works at full speed again.

Could it just be that it all goes through Telekom Slovenije who does some weird load balancing? Definitely worth an investigation, but ZPS might be a better address for this than AKOS.

Telemach is also funny in net-neutrality regard:

Article 7.2 of their terms of service https://telemach.si/download/terms/splosni-pogoji-poslovanja...

> Naročnik se obvezuje, da po priključitvi na omrežje izvajalca: > ... > * ne bo postavljal strežnikov na svoji lokaciji, razen v primeru sklenitve ustreznega dogovora z izvajalcem, > ...

It states that customers are bound not to setup servers on their internet connection point without prior aproval by the ISP. It sounds against the law to forbid this, albeit ianal.