mail/claws-mail: IPv6 issues: SSL handshake error

Hello,

I'm using mail/claws-mail for my daily work with FreeBSD (CURRENT, 14-STABLE at this time).
After switching to a working IPv6 environment I face serious connection problems with one of
my providers, to which claws-mail prefereably connects via IPv6. Sending and receiving is done
via  "Use TLS" on sending an receiving (the provider, goneo.de has a dedicated introduction
configuring claws-mail I followed step by step).

On the firewall I observe that the provider in question is connected via IPv6, while other
providers, University and others, are not, they are still with IPv4 and do not show any issues.

claws-mail provides a log screen, but I can not make much out of it, the SMTP and/or IMAP
server is connected at the correct port and the initial handshake seems all right, but in 8
out of 10 times the connection fails and does not get initialized due to a "TLS handshake
error". Sending emails takes sometimes 10 attempts, but then of a sudden it works flawlessly!
After running claws-mail for a couple of minutes a day, this problem seems to go away in a
mysterious way, receiving/sending works like a charm as nothing has ever been broken before
...

I;m floating here like a dead man in the water. The firewall / router is FreeBSD / ipfw, I
suspected this instance, but why should mail being blocked/corrupted while other connections
via IPv6 work?

Maybe someone has some ideas what to check and where to look ...

Thanks in advance,
oh 


-- 

A FreeBSD user