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Tom Johnson avatar Server

RFC5321 and multiple RCPT TO

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Tom Johnson

After analyzing https://datatracker.ietf.org/doc/html/rfc5321 I've got impression that some of its fragments contradict each other.

A single notification listing all of the failed recipients or separate notification messages MUST be sent for each failed recipient. For economy of processing by the sender, the former SHOULD be used when possible.

seems to contradict:

Addresses that do not appear in the message header section may appear in the RCPT commands to an SMTP server for a number of reasons. The two most common involve the use of a mailing address as a "list exploder" (a single address that resolves into multiple addresses) and the appearance of "blind copies". Especially when more than one RCPT command is present, and in order to avoid defeating some of the purpose of these mechanisms, SMTP clients and servers SHOULD NOT copy the full set of RCPT command arguments into the header section, either as part of trace header fields or as informational or private- extension header fields.

Do they actually contradict each other or am I missing something?

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Håkan Lindqvist
Please elaborate on what the perceived contradiction is. I do not immediately understand how these two quoted sections even relate to each other, much less contradict one another.
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Tom Johnson avatar
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Tom Johnson
I interpreted RFC incorrectly, anx's responses got directly to the source of my confusion. But thank you for taking your time.
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anx avatar Server
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anx

Different reasoning for the message itself - and notifications regarding that message.

The part where spelling out unmentioned recipients in the headers defeats the purpose refers to the message as it is transmitted to the recipients.

The notification about failed recipients goes back to the sender, who clearly at one point must have known all recipients addresses anyway.

  • Telling the sender that some - even unmentioned in the message structure - recipients have not received the message? A-okay.
  • Telling the recipients the full list of other recipients, after the addresses were deliberately kept out of the message structure? Not okay.
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