Document how to test that outgoing port 25 connections work

[link2xt]

There is a thread about it on the forum:
https://support.delta.chat/t/secure-join-between-accounts-on-separate-chatmail-servers/2932

Hetzner has FAQ entry:
https://docs.hetzner.com/cloud/servers/faq/#why-can-i-not-send-any-mails-from-my-server

DigitalOcean documentation:
https://docs.digitalocean.com/support/why-is-smtp-blocked/

[missytake]

An online test which tries to connect to port 25 of some mail server from the chatmail server maybe?

[link2xt]

A test getting nine.testrun.org banner would be fine I guess, or some other server like fastmail.

But in any case readme needs a step together with getting DNS name and hosting.

[missytake]

A, 2 chatmail operators report that the test_no_vrfy routinely fails for them because it tries to connect to port 25 and it is blocked.

[link2xt]

2 chatmail operators report that the test_no_vrfy routinely fails for them because it tries to connect to port 25 and it is blocked.

This issue is specifically about outgoing port 25, testing that the server can send outside over port 25.

test_no_vrfy is about accepting incoming connections and users failing to connect over port 25 to their server from local machine. Changing this test or skipping it by default should be a separate issue.