[Users] [Bug 4649] New: Claws Does Not Attempt To Use IPv4 Protocol If IPv6 Protocol Is 'Broken'

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https://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=4649

            Bug ID: 4649
           Summary: Claws Does Not Attempt To Use IPv4 Protocol If IPv6
                    Protocol Is 'Broken'
           Product: Claws Mail
           Version: 4.1.1
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Other
          Assignee: users at lists.claws-mail.org
          Reporter: dustbiz at gmail.com

When attempting to send or receive email via a server with a non-functioning
IPv6 protocol, Claws Mail (CM) fails rather than attempting to use the
functioning IPv4 protocol.

Steps to Reproduce:

1. Have a system that:

a) is connected only to a server / gateway that is set up to handle both IPv4
and IPv6 protocols, and where the IPv4 protocol is functioning normally but the
IPv6 protocol is 'broken'.

b) has CM installed with IPv6 compatibility enabled.

2. Attempt to send or receive email.

Actual result: CM fails, giving a time-out error.

Expected result: CM will attempt to use IPv6 but if that fails, it will use
IPv4 to successfully send / receive email.

Potentially helpful related information:

1. This looks like it could be the GTK3 version of Bug #3244.

2. The 'traceroute', 'dig', and 'nmap' utilities seem to be able to produce
their respective 'expected results' on the above-mentioned system without
needing to use an option to specify the IPv4 protocol.

3. The 'telnet' and 'openssl' utilities seem to fail in the same way as CM on
the above-mentioned system (assuming they are not using the option to specify
the IPv4 protocol). (When using the option to specify IPv4, they both work as
expected.)

4. Workaround #1 (untested): Build CM with IPv6 compatibility disabled.

5. Workaround #2 (tested OK): Create / edit the '/etc/gai.conf' file so it has
the following line:

precedence ::ffff:0:0/96  100

My understanding is that this will direct the system to give precedence to
using the IPv4 protocol.

6. Here is an email I sent to the users list with more details on the testing I
did to troubleshoot this:
https://lists.claws-mail.org/pipermail/users/2022-October/031115.html .

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