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

[Dustin Miller]

On Wed, 12 Oct 2022 02:18:02 +0200
mi <codejodler at gmx.ch> wrote:

> There is actually a faint chance that your mail servers mail ports
> are blocked. Not probable but also not impossible ...
> 
DM: Thanks, mi, the additional ideas and tool mentions are quite
helpful. I know the 'local' IT guy said he hadn't changed any settings,
but I also know from past experience that an ISP can remotely change
settings on their clients' devices. I guess there's also the settings
they control at the various 'hubs' along the way before they connect to
the 'outside' internet. Anyway, I'll try some of these different things
when I have a bit more time, and see what I can figure out. Thanks
again, ---Dustin
> 
> 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.
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