On Wed, Dec 04, 2024 at 12:22:20PM +0100, Renaud Allard via mailop wrote:
>
>
> On 12/4/24 12:00 PM, Cyril Nicodeme via mailop wrote:
> > Hi everyone,
> >
> > I was wondering if there was a standardized limit, or a "common sense"
> > limit on how many (valid) RCPT command a client can send. If they want
> > to send an email to a thousands recipients that are on the same MX
> > server, would they be able to do that in one session or would they have
> > to split the number of MAIL FROM/RCPT TO/DATA commands ?
> >
> Technically, RFC speaking, there is no maximum number of recipients.
> However, many implementations will block over a certain amount.
> For example, Z/os can accept 2000 recipients, but Amazon AWS SES will limit
> to 50.
> Also, RFC5321 Sec. 4.5.3.1.8 requires that an MTA supports at least 100
> recipients. But as you can see, Amazon doesn't respect that.
> To be on the safe side, you should consider to limit sending to 50 or 100
> recipients at once.
> That said, if you send more than allowed, the MTA should give you a 421
> response (still following RFC5321).
No, not a "421", since that would normally also be a connection abort,
and none of the recipients would get the mail. Rather, the correct
handling is to softfail the excess recipients and accept the initial
batch that came in under the count.
A server that drops the connection on too many recipients (especiall if
under 100) is in gross violation of the spec, and the community should
not accomodate their disrespect for basic interoperability guidelines.
--
Viktor.
_______________________________________________
mailop mailing list
mailop@mailop.org
https://list.mailop.org/listinfo/mailop
