SendGrid: duplicate Message-IDs with merge_data/batch send about django-anymail HOT 2 CLOSED

SendGrid does not handle merge fields (sub vars) in the Message-ID header.

from django-anymail.

Actually, it turns out SendGrid does the same thing if you let them generate their own Message-ID: they use the same Message-ID for all individual recipient emails in the batch. So there's no way to avoid this behavior with SendGrid's current functionality.

And the "duplicate" Message-IDs are probably OK, because the sender get to decide whether or not two emails are "the same message" under RFC 2822 [emphasis added]:

Note: There are many instances when messages are "changed", but those
changes do not constitute a new instantiation of that message, and
therefore the message would not get a new message identifier. ...
In all cases, it is the meaning that the sender
of the message wishes to convey (i.e., whether this is the same
message or a different message) that determines whether or not the
"Message-ID:" field changes, not any particular syntactic difference
that appears (or does not appear) in the message.

Closing as not an issue.

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