Message-ID: / In-Reply-To: ID continuity through mail servers
We have a project to write an automated email client which is required to
link reply messages sent back in response to its original message, what is
the best method to provide this linkage? I am using Postfix (2.11) as my
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?
Will a reply from the Destination mailbox using MS Outlook contain the
unaltered original message ID in the In-Reply-To: field?
Is there a mail server standard around Message-ID: / In-Reply-To: formatting
that would support using Message-ID: and In-Reply-To: to form the original
-> reply linkage?
We have read many articles about other mail servers which alter the
Message-ID: field outbound to mask the client identity somewhat (not reveal
internal host names for example).
Is there a list somewhere which talks about the Message-ID: integrity
between Postfix and various platforms?
Our end goal is to ensure that the originating mailbox gets a response that
it can marry up to the reply in the event that more than one message has
been sent to the destination and one or more replies received from that
> On May 5, 2017, at 8:16 AM, Richard Sass <[hidden email]> 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