Update (or remove) some manual Thunderbird tests

We have a manual test that relies on having access to a non-anonymizing SMTP relay, i.e. a SMTP relay that writes the IP address of the client it is relaying email for in the Received header: check that Thunderbird really torifies SMTP connections, by looking at the Received header → that’s not necessary anymore since the corresponding automated tests have the check_tor_leaks tag so a proxy + firewall bypass would be noticed.

And we also check that the EHLO/HELO SMTP message is not leaking anything at the application level, that currently relies on using a SMTP relay that either supports non-TLS connections (emma peel tells me she could not find one) or that supports StartTLS. emma peel suggested we drop the first option that’s impractical and I agree… unless there are common .onion SMTP services without TLS (Riseup?).

The manual test suite is: https://tails.boum.org/contribute/release_process/test/

The branch should be based on master so we can merge it without waiting for a specific release.

Related issues

• Blocks #16209

Original created by @intrigeri on 15914 (Redmine)