Op 14-11-2023 om 17:44 schreef Kees van Vloten:
I did another test: I have just downgraded the dovecot packages to
the version in Bullseye, i.e. 2.3.19 -> 2.3.13, without making any
other change.
This solved the issue! Thunderbird (which was not even restarted) can
now send mails again.
Unfortunately it is not such a good solution as I would rather have
more recent packages :-)
@aki, do you still think the culprit is in the client?
I'd say the client is the culprit. From what I can tell it is sending: AUTH
GSSAPI <Enormous initial response>
This is not allowed. The initial response can only be used when the AUTH
command stays small enough to fit in a regular SMTP command line. If it is
bigger the client should do the following:
client> AUTH GSSAPI
server> 334
client> <Enormous initial response>
etc..
Further explained in RFC 4954, Section 4:
The optional initial response argument to the AUTH command is
used to save a round-trip when using authentication mechanisms
that support an initial client response. If the initial
response argument is omitted and the chosen mechanism requires
an initial client response, the server MUST proceed as defined
in Section 5.1 of [SASL]. In SMTP, a server challenge that
contains no data is defined as a 334 reply with no text part.
Note that there is still a space following the reply code, so
the complete response line is "334 ".
Note that the AUTH command is still subject to the line length
limitations defined in [SMTP]. If use of the initial response
argument would cause the AUTH command to exceed this length,
the client MUST NOT use the initial response parameter (and
instead proceed as defined in Section 5.1 of [SASL]).
Regards,
Stephan.
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