How about this:
Errors due to exceeding these limits may be reported by using the
reply codes. Some examples of reply codes are:
452 Too many recipients (see below)
RFC 821 [30] incorrectly listed the error where an SMTP server
exhausts its implementation limit on the number of RCPT commands
("too many recipients") as having reply code 552. The correct reply
code for this condition is 452. Clients SHOULD treat a 552 code in
this case as a temporary, rather than permanent, failure so the logic
below works.
When a conforming SMTP server encounters this condition, it has at
least 100 successful RCPT commands in its recipients buffer. If the
server is able to accept the message, then at least these 100
addresses will be removed from the SMTP client's queue. When the
client attempts retransmission of those addresses which received 452
responses, at least 100 of these will be able to fit in the SMTP
server's recipients buffer. Each retransmission attempt which is
able to deliver anything will be able to dispose of at least 100 of
these recipients.
If an SMTP server has an implementation limit on the number of RCPT
commands and this limit is exhausted, it MUST use a response code of
452 (but the client SHOULD also be prepared for a 552, as noted
above). If the server has a configured site-policy limitation on the
number of RCPT commands, it MAY instead use a 5XX response code.
This would be most appropriate if the policy limitation was intended
to apply if the total recipient count for a particular message body
were enforced even if that message body was sent in multiple mail
transactions.
