Outbound trafic on port 25 is catched by Swisscom's SMTP relay/server

Fludoviek72

I was trying to set up a mail server at home when I realized that swisscom intercepts everything that leaves port 25 (https://en.wikipedia.org/wiki/Message_transfer_agent) so I can't send any email from my server to anything that's not Gmail or Yahoo.

You can check this by trying to telnet Protonmail's SMTP server:

telnet mail.protonmail.ch 25

The IP is supposed to be 185.205.70.128 but who replies? Swisscom! By putting their SMTP server in front of it! So I can't send emails to Proton, Tutanota or other "unknown" email service providers that aren't Google or Yahoo.

220 nwas.bluewin.ch vimdzmsp-nwas04.bluewin.ch Swisscom AG ESMTP server ready

I'd like to know if there's any way to prevent swisscom from man-in-the-middleing port 25.
Don't tell me to use another port because then you would have to convince every MTA to change the SMTP port 🙂
And don't tell me it's to prevent spam too.

Also has anyone managed to get a reverse dns record changed? I'm on a residential subscription.

Thanks in advance.

bitracer

Have you tried SMTP over TLS?

Fludoviek72

When I use TLS it doesn't work
When I use plaintext it doesn't work

postfix error

2DF4A464D63: TLS is required, but was not offered by host mailsec.protonmail.ch[176.119.200.129]

bitracer

On the port 587 or 465?

Fludoviek72

I can't use any port other than port 25. Otherwise I'd have to convince all the mail providers and hoster to change port.

bitracer

Find a third party mail provider that can relay the email for you. The port 587 is a standard port for SMTP over TLS.

Fludoviek72

I will try to setup an SMTP relay, I still find it strange that Swisscom intercepts everything.

Fludoviek72

I should contact them, they might be able to do something. Can i contact Swisscom with a mail

Thx for your help

Fludoviek72

If there is a Swisscom technician who comes by, do you know if you can resolve the problem?

bitracer

https://www.swisscom.ch/en/residential/help/contact.html

gasoo

The interception of Port 25 on Swisscom Residential Internet is active for more than 10 years if I am not mistaken.
There is no easy way around that.

Furthermore, even if you manage to circumvent Port 25 Interception, you still have the following issues:

- PTR Records are static and can not be changed.

- The IP Range is classified as Dynamic/Residential.

- No static IP is possible with Residential

It might work to operate a Mailserver on Residential but you will have some troubles communicating with a lot of Mailservers.

I would say, switch to Business Internet or get a vServer somewhere, so that you have a static IP, no interception, a static and matching PTR and finally a IP that is not classified as Dynamic/Residential.