From Newsgroup: muc.lists.freebsd.ports

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Hello,

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

On the firewall I observe that the provider in question is connected via IP= v6, 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 SM=
TP 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 be=
en broken before
...

I;m floating here like a dead man in the water. The firewall / router is Fr= eeBSD / 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=20


--=20

A FreeBSD user

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From Newsgroup: muc.lists.freebsd.ports

Op 28-08-2025 om 17:16 schreef A FreeBSD User:

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

Hi,

Does it work with this provider if you force claws-mail to use ipv4?

Can you reproduce the issue easily? Is it possible to reproduce it with openssl?
Something like this. There are also options to choose specific TLS versions. openssl s_client -starttls imap -connect <imap-server>:143 -6
openssl s_client -starttls smtp -connect <smtp-server>:25 -6

Can you tcpdump the traffic to a file and see in wireshark what is going on?

Regards,
Ronald.



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From Newsgroup: muc.lists.freebsd.ports

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Am Tage des Herren Thu, 28 Aug 2025 18:49:41 +0200
Ronald Klop <ronald@FreeBSD.org> schrieb:

Op 28-08-2025 om 17:16 schreef A FreeBSD User:

Hello,
=20
I'm using mail/claws-mail for my daily work with FreeBSD (CURRENT, 14-S=

TABLE 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. Sen=

ding 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).
=20
On the firewall I observe that the provider in question is connected vi=

a IPv6, while other

providers, University and others, are not, they are still with IPv4 and=

do not show any

issues.
=20
claws-mail provides a log screen, but I can not make much out of it, th=

e 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 t=

o a "TLS handshake

error". Sending emails takes sometimes 10 attempts, but then of a sudde=

n it works

flawlessly! After running claws-mail for a couple of minutes a day, thi=

s problem seems to

go away in a mysterious way, receiving/sending works like a charm as no=

thing has ever been

broken before ...
=20
I;m floating here like a dead man in the water. The firewall / router i=

s FreeBSD / ipfw, I

suspected this instance, but why should mail being blocked/corrupted wh=

ile other

connections via IPv6 work?
=20
Maybe someone has some ideas what to check and where to look ...
=20
Thanks in advance,
oh
=20
=20

=20
=20
Hi,
=20
Does it work with this provider if you force claws-mail to use ipv4?
=20
Can you reproduce the issue easily? Is it possible to reproduce it with o=

penssl?

The problem itself as described can be reproduced with claws-mail utilizing=
IPv6 - for me at
least - on CURRENT. But there is a certain speciality: my home office box u= ses IPv6 via prefix
delegation in a subnet, at work we use OPNsense with NPTv6 - which doesn't=
introduce any
problems, although claws-mail prefers IPv6 (other provider there than thos =
of mine at home).
Just a "descriptive" statement.

Did not try openssl so far, but thank you for the hint!

Something like this. There are also options to choose specific TLS versio=

ns.

I do not see such in claws-mail config, options are NO TLS, TLS, STARTTLS w= hich refers to the
proper port when autoconfigured. Manually override can be applied.

openssl s_client -starttls imap -connect <imap-server>:143 -6
openssl s_client -starttls smtp -connect <smtp-server>:25 -6
=20
Can you tcpdump the traffic to a file and see in wireshark what is going =

on?

Haven't done the wireshark analysis so far, but did a lot of tcpdumps both = sides of the end of
the communication between host and router, but it seemed all clear to me an=
d faults at the
provider's side ... But, I have to admit that in terms of networking, I'm a=
kind of an enduser
...

When forcing claws mail to use IPv4 only, everything is all right. There is=
also not problem
when using NPTv6 on my FreeBSD routing/ipfw instance.=20

In the faulty case, the puzzling thing is that after a couple of time runni=
ng claws-mail, say,
20 - 30 minutes doing some mail fetches and sending (even with the nasty re= plying on faults)
everything runs smooth - until next restart of the application. And this lo= oks to me like some
serious misconfiguration or serious issue on the providers side.=20

=20
Regards,
Ronald.
=20
=20

--=20

A FreeBSD user

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