Re: [exim] How can exim do this?

On 03/03/2015 02:56, helices wrote:
> I am tasked to design, build and maintain a new MTA. The company has
> one special requirement, for which I'm investigating the simplest
> solution:
>
> For each incoming message received, every outgoing "reply" must use
> the "To:" address from the incoming received message as the "From:"
> address in the outgoing reply.
>
> This is trivial when the incoming has "To: sally@???," Sally
> reads and replies, and the outgoing message has "From: sally@???"
>
> It's trickier when the incoming has "To: info@???," the MTA
> delivers to an Exchange server, which distributes that message to
> Sally, and Sally replies. What is the simplest way for that outgoing
> message to use "From: info@????"
>
> Scope is roughly one hundred (100) different domains and, possibly,
> thousands of combinations with various username@???.
>
> Ideally, the MTA will handle all of header address processing,
> whatever that process might look like. I seek the simplest solution,
> regardless how that process looks and compares to the status quo.
It's doable, but would require a fair bit of work and really isn't
something exim would/could do directly.

However, I would implement the task as a message filter; for each
message, extract the envelope to: address, the message id, and the
time/date stamp, adding them to a database (local copy of sqlite3 would
do fine for this, or mysql/postgres if you want it to scale better).
Then *if* the message is effectively outbound (from a local domain
address) AND has an in-reply-to header, use that to look up the original
email and perform the rewrite.

Not THAT hard, but still at least three or four days coding.

Another solution (and what I do for a matching but simpler situation) is
to use a mail client that can already do this - Thunderbird (for
example) can and does search aliases for the "to" address and preselects
one (if it can find a match) for the outbound. Then the answer
simplifies to "any MTA you choose" :)