[exim] Exim as transparent Rewrite Gateway

Hi Community,

I am currently working on a project for a transparent Rewrite Gateway which shall mask two independent Exchange Organizations behind a third domain. First I tried to solve this task by using a Postfix server, but Postfix was not able to rewrite the "From" and "To" the way the gateway is a completely independent black box, because incoming mail got a rewritten "To" field, but the mail was still delivered with the new domain suffix of which the internal mail server don't know anything from.

I used the following functions from Postfix:

* generic (outgoing - running fine except for meeting requests, which are ignored by the gateway)
* canonical (incoming - rewrite is done an mail gets transported fine, but the internal Exchange server receives a mail for @newcorp.com and loops it back to the gateway)
* header_checks (incoming - same behavior like canonical, the log looks fine but the mails get delivered with the wrong suffix)

Till now I was not able to solve my issues with Postfix and I hope, that Exim will be a better choice for my project. Can you tell me if it is possible to solve my issues with Exim to create a real rewrite gateway? If it is not possible, do you have some more information for me on why it can't be done?

My Gateway shall:

* Relay domains @internal1.com and @internal2.com to extern as @newcorp.com
* Rewrite incoming mails from @newcorp.com to @internal1.com or @internal2.com
* Transport mails to both internal organizations
* Exclude S/MIME encrypted and/or signed mails from rewriting
* Besides regular mail the gateway also needs to rewrite meeting requests and other types of mails coming from and to an exchange server

Thank you all in advance for your input and your thoughts!

With best regards
Dennis Weber