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From: Viktor Dukhovni (postfix-usersdukhovni.org)
Date: Fri May 03 2013 - 08:32:07 CDT
On Fri, May 03, 2013 at 02:25:15PM +0200, Ralf Hildebrandt wrote:
> Section 126.96.36.199 of RFC 2821 (188.8.131.52.10 in RFC 5321) recommends to treat
> a 552 response after the RCPT TO command as if it was actually a 452
> response. This behaviour was intended for cases where the number of
> recipients exceeds the MTA's limits, and the idea was that the sending
> MTA should requeue the extra recipients.
RFCs have bugs, this is one of them. In practice MTAs don't return
552 for "too many recipients", and the 552->452 mapping creates more
problems than it solves.
> Section 6.4 of RFC 1870 contradicts this, and explicitly says that a
> 552 response must not requeue the recipient. This is intended for cases
> where the message size limit is imposed on specific recipients.
> So generally, the smtp response code 552 can be used for multiple
> incidents, like the recipient count and also for the message size. In
> order to address this kind of issue on the Email Security appliance, we
> have logged a 'defect' with number ...... "Per-recipient rejection based
> on message size in response to a RCPT command", and our engineering team
> is working on an implementation which works in all cases that all
> messages get soft or hard bounced correctly without any issues.
In the interim you can use 554 5.2.2 ... which won't be misunderstood.