[Users] Claws Mail Can't Connect to Internet With Specific Internet Connection

[mi]

Dustin,

There is actually a faint chance that your mail servers mail ports are blocked. Not probable but also not impossible ...

You can find out e..g by a telnet, like Paul Rolland already suggested, on ports 465, 995 or whatever youre claws is configured to use.

Or you might run an nmap (a commandline tool, installable package) and see what it shows. Just the default scan would be enough to see what ports are open.

~ mi: nmap mail.gmx.net
Starting Nmap 7.92 ( https://nmap.org ) at 2022-10-12 02:08 CEST
Nmap scan report for mail.gmx.net (212.227.17.190)
Host is up (0.024s latency).
Other addresses for mail.gmx.net (not scanned): 212.227.17.168
Not shown: 990 filtered tcp ports (no-response)
PORT     STATE  SERVICE
25/tcp   open   smtp
80/tcp   closed http
110/tcp  closed pop3
143/tcp  closed imap
443/tcp  closed https
465/tcp  open   smtps
587/tcp  open   submission
993/tcp  closed imaps
995/tcp  closed pop3s
2000/tcp closed cisco-sccp

( Their POP server 'pop.gmx.net' has open ports 110/tcp and 995/tcp )

For more extensive scans yiou might try options like -A or -T4

A successful telnet would look like

> telnet pop.gmx.net 110
Trying 212.227.17.169...
Connected to pop.gmx.net.
Escape character is '^]'.
+OK POP server ready H migmx101 1N6LUP-1pFwre0ZQX-017CmE

Why do i suggest it ... in Germany, the very popular ISP Telecom usually also provides the router to households and they have some firewall stuff there. Some years ago, they suddenly came up with the great idea to install a whitelist of allowed email servers. You could disable that feature, or add your own servers, but i guess most people never even got aware of it since they used one of the 'allowed' ones (including, of course, Telecom).
Just to demonstrate how dumb things can get.