On Thu, 26 Mar 2015 10:12:22 -0500 (CDT)
Dave Funk <dbf...@engineering.uiowa.edu> wrote:
If they are compatible you respond with a 250, if not with a 452 (or
other 45* type reply).
On 26.03.15 11:52, David F. Skoll wrote:
We looked at doing this. There are some serious downsides:
1) Some senders (for example, mailing list tools) send to quite a number
of recipients at once. 30 or even 100 is not out of the question.
If all of them have different policies, the last recipient is going to
wait a very long time indeed to receive his or her email.
FYI: all SMTP RFCs yet require accepting at least 100 recipients at once.
(I don't want to discuss this, just to note...)
in such case, either spam is refused with sane defaults, or mail is accepted
and should be handles as accepted (e.g. delivered to spam folder).
2) Some marginal SMTP software (old versions of Novell Groupwise, I
think? Can't recall exactly) does not handle 4xx responses to RCPT:
very well. It basically converts them to 5xx.
that is very old (and very broken) SMTP software, and since 4xx code can
result because of different issues, I don't think we should take this into
account
3) You have no control over the retry interval or retention time on the
SMTP client. It's not unimaginable that some messages simply won't get
delivered because the SMTP client gives up. Some SMTP clients use
an exponential backoff algorithm rather than a constant retry interval,
and that can be disastrous in this situation.
clients with exponential backoff interval should be safe here... the others
might not :-)
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