We're migrating from Exchange 2003 to Zimbra, and as such are running the two systems in parallel. Since both of our emails are authoritative for the same domain (e.g. "example.com"), we use a complex method to get them to talk to eachother. Here's the layout:
| Internet |
| Gateway |
| Exchange | | Zimbra |
The gateway is just a Postfix system that does some address mangling and routes outside emails. When the gateway receives an email for "firstname.lastname@example.org" it routes it to Zimbra, and when it receives an email for "email@example.com" it routes it to Exchange. No problems here at all.
The Gateway is set as the smart host relay for both Zimbra and Exchange so outbound emails also go through the Gateway. So that they can talk to eachother, we have two fake domains - "zimbra.example.com" and "exchange.example.com". When someone in Zimbra sends an email to someone in Exchange, they actually send to "firstname.lastname@example.org". The Gateway mangles the "exchange.example.com" to "example.com" and delivers to Exchange. The same thing happens the other way, except the users in Exchange send to "email@example.com" and the Gateway mangles and delivers to Zimbra.
Again, there is no problem with this method.
Here's where the problem lies though... In Exchange, we "forward" from the users mailbox using the Exchange forward feature on the Active Directory record. The only way this works in Exchange is to create a contact first with the destination address (i.e. "firstname.lastname@example.org"), then you forward to that contact. This works perfectly fine - for the vast majority of emails.
However, there are a small number of emails that bounce with "Body Content Type not supported". This only occurs from Exchange to Zimbra. We traced the problem to potentially an 8BITMIME issue, so we watched the raw network traffic. It looks like Exchange connects, issues an EHLO, and then just disconnects! It doesn't even try to send the email. The server does advertise "250 8BITMIME" so it should be at least trying to send it. It seems like it's a bug with the Exchange Contacts (many people seem to be reporting this).
Does anyone have any ideas on how to force Exchange to deliver the mail?