You are right Victor of course...
And for the record, ESP's and senders should NEVER assume that they can
send even 100 recipients.. In our MagicMail SMTP we apply a penalty for
invalid users.. each invalid user is the equivalent of 15 legitimate
recipients.. so if you send 10 invalid recipients, you quickly hit the
session sending limits.. (Of course we have rate limiters on top of the
per session limits)
And PIPELINING should go the way of the DODO..
Senders should carefully watch for the response code on every RCPT TO,
and IF you are an ESP that gets a 452, stop trying to send to more RCPTS
in the same session.
(Even though MagicMail doesn't advertise PIPELINING, amazing how many
try to PIPELINE anyways.)
On 2024-12-04 21:09, Viktor Dukhovni via mailop wrote:
On Wed, Dec 04, 2024 at 08:01:34PM -0600, Grant Taylor via mailop wrote:
On 12/4/24 09:45, Viktor Dukhovni via mailop wrote:
No, not a "421", since that would normally also be a connection abort,
and none of the recipients would get the mail.
What do you think about a 450 4.2.1?
Well, the correct reply code is 452. The correct enhanced status code
is 4.5.3:
https://www.iana.org/assignments/smtp-enhanced-status-codes/smtp-enhanced-status-codes.xhtml
Rather, the correct handling is to softfail the excess recipients and
accept the initial batch that came in under the count.
Please clarify what you mean by "softfail" in this context. I've seen
different things and would hate to assume incorrectly.
A 4XX response, such as: 452 4.3.5 ...
Now an MTA will typically impose a smaller limit (than 100) on the count
of *invalid* recipients before the connection is closed with 421 or 521.
That is so long as the recipients are essentially all valid, it should
accept 100 + some tolerance for pipelining to have sent a bunch more,
before the first 452 was noted in response. Once enough of the
recipients are bad, abuse prevention kicks in and the RFC lower-bound
ceases to be the primary concern.
--
"Catch the Magic of Linux..."
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Michael Peddemors, President/CEO LinuxMagic Inc.
Visit us at http://www.linuxmagic.com @linuxmagic
A Wizard IT Company - For More Info http://www.wizard.ca
"LinuxMagic" a Reg. TradeMark of Wizard Tower TechnoServices Ltd.
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