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

[Dustin Miller]

On Thu, 13 Oct 2022 16:59:13 +0200
Paul Rolland <rol at witbe.net> wrote:

> Waoh !!! Thanks so much for the detailed report, with all your
> findings !
> 
DM: You're welcome, Paul.
> 
> Yes, V4 and V6 can cause what you have experienced. The exact reason
> is yet to be understood, and some reasons could be:
>  - system update (on your machine) that triggered some IPv6 autoconf
> and then your machines "thinks" it can use a broken IPv6,
> or
>  - IPv6 from your ISP was working perfectly but something went wrong,
> and because no one really cares, it is still broken now and you are
> affected, or
>  - someone changed some IPv6 filtering rules and only the ones (few
>    apparently) using IPv6 are affected, no enough to ring a bell
> somewhere and have it fixed.
> 
> traceroute has an option (-4 or -6) to select which IP version you
> want the traceroute to be done. telnet does too, and openssl (BTW,
> openssl is not using telnet under the hood ;).
> 
DM: Good to know. :) I discovered these options for telnet and openssl
and that's how I forced IPv4 on them during my testing to help isolate
the issue. I didn't explore the same with traceroute because it used
IPv4 by default, but it's good to know the option is there. I tried
traceroute just now w/ IPv6 for pop.gmail.com and it only gives one IP
address as output, which seems to belong to our ISP. This is in
contrast to lots and lots of different IP addresses given when I ran
the same test with the default IPv4. So presumably that means it's an
issue at the ISP-level that we likely don't have any direct control
over. Appreciate the additional input, ---Dustin
> 
> So, if you really want to go further, you can activate these options
> when testing the LAN access. You should see a real difference, and
> that should help highlight the problem.