Dave CROCKER wrote:
First blank line after DATA.
Whether that affords sufficient value-add is an open question to me and
There is no doubt it has value whether you got it at DATA (up to the
first blank) or received the entire payload.
The difference is a question of overhead savings which SMTP does not
allow because a receiver can not DROP at the first blank due to some
clear DKIM/SMTP verification/policy failure. To do so creates an
implicit 451 retransmission problem.
See the discussion in IETF-SMTP about this very issue:
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