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Re: [ietf-smtp] SMTP Retrying/Sending Strategy on 452 / 4.5.3

2019-02-11 11:08:36
Richard Clayton <richard(_at_)highwayman(_dot_)com> writes:

Servers often impose 100 recipient/message limits in order to discourage
less sophisticated spammers from misbehaving at scale. You would be
unwise to build a sending platform that expected to be able to send
email with more than 100 recipients per destination

I ran into my favorite version of that problem somewhere around 2010.  The
antivirus software we were using at the time (I think Sophos, although
don't quote me on that) decided that it should inspect all outgoing SMTP
network transactions to look for viruses.  Not a completely unreasonable
thing to do.  However, the SMTP code had a bug or misfeature such that if
the message was going to more than (IIRC) 50 recipients, it would just
silently eat the message.

Not return an error, not indicate any sort of failure, just silently
/dev/null the message.

Given that the message that people were trying to send was the acceptance
and rejection messages to prospective college kids, this caused quite a
lot of consternation and emergency attempts to debug the campus mail
servers until we figured out it was the antivirus.

Russ Allbery (eagle(_at_)eyrie(_dot_)org)              

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