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Re: [ietf-smtp] SMTP Reply code 500

2020-03-04 08:58:02

--On Wednesday, March 4, 2020 09:33 +0000 Paul Smith
<paul(_at_)pscs(_dot_)co(_dot_)uk> wrote:

A buggy SMTP server could send an invalid response to the SMTP
client  (ie a response not starting with a three digit number
beginning with 1 to 5). In that case, the SMTP client should
do whatever it wants to do, ranging from ignoring it, to
dropping the connection in disgust and reporting an error to
the user/administrator/log/whatever (I'd probably advocate for
the latter).

In the interest of cleanliness (i.e., the fact that they are
breaking the rules doesn't mean I should, even if I'm
disgusted), I would probably advocate for sending a QUIT command
prior to dropping the connection, but yes.

Certainly trying to continue a session with a server that is
badly implemented enough, or has gotten confused enough, to send
responses that don't start with a digit in the 1-5 range would
be ill-advised.


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