Date: Mon, 13 Apr 2020 01:05:54 -0400
From: "Valdis Kl=?utf-8?Q?=c4=93?=tnieks" <valdis.kletnieks@vt.edu>
Message-ID: <477754.1586754354@turing-police>
| But if it already knew that it would need two transactions, why did it
bother
| with the first transaction?
To verify that both addresses are OK. Whatever sequence it uses,
3 SMTP transactions are needed, one to validate the first address,
(and optionally the second), one to deliver to the second address
(also validating it if that wasn't done in the first) and one to
deliver to the first addr.
There could be one less RCPT TO transaction than is currently used,
but only when there are just 2 deliveries needed, add a 2nd Bcc
recipient, and now 3 separate delivery SMTP connections are needed,
plus verification - if all 3 addresses are verified in the first
connect, a total of four, any other sequence and more are required.
Hence, verify everything in the first transaction, and once we know
all addresses are OK, deliver to them in one transaction for all visible
recipients (if all are, this can be a continuation of the verification
connection - which is the usual case) and one more for each bcc recipient.
| Or is the problem that if the first transaction sends 1 bcc note
| and succeeds, and the second sends 3 successful and one failed,
| error recovery gets difficult?
Yes. Whichever order those two are done. I believe though that
the three and one case ends up in no deliveries - I think you'll find
that if there are any failures (even temporary ones) to any of the
RCPT TO commands (or MAIL FROM obviously) then MH's SMTP agent quits,
and never sends a DATA command. It sends to everyone or no-one.
| (Though even if you have no bcc's, and 2 recipients to 1 mx,
| and 2 recipients to a different mx, and one fails, you still
| have the same problem...)
Yes, but recall than when MH was developed, for 99% of e-mails, all
recipients were on the local system, networking was still (mostly)
a coming thing, for the vast majority of users.
| Or has it been doing a pre-test all along and I've just never
| caught it at it? :)
Yes, always - but when there are no BCC recipients, then there's no
need for separate SMTP transactions, and once the pre-test is done,
we can simply complete the transaction with a DATA command, This
separate SMTP series is only needed when we're hiding recipient addresses,
so one SMTP transaction cannot be shown all of them.
kre