> On May 5, 2017, at 8:16 AM, Richard Sass <richard.s...@seqent.com> wrote:
>
> For a simple example using Postfix and our application as the client sending
> will the “Message-ID:” outbound from my application message be retained as
> it passes through Postfix, unaltered arriving at the destination mailbox on
> the same Postfix server?
Yes. Altering Message-ID headers breaks "threading" in mail clients and
makes message tracking more difficult. Postfix does not alter message ids,
nor should any other MTA.
> Will a reply from the destination mailbox using MS Outlook contain the
> unaltered original message ID in the “In-Reply-To:” field?
Likely so. That header is typically supported, and contains just
the message id of the original message.
Things are a bit more complicated with the "References" header,
after sufficiently many messages back and forth the "References:"
header may get too long to fit in one SMTP maximum length (998
bytes) line, and "folding" may "corrupt" some of the ids in the
"References:" header. It would be prudent of MUAs to keep only
a small number of the most recent "References:" elements, or fold
the header properly, but I don't know whether any/which MUAs do
that.
--
Viktor.
