Zimbra in parallel with exchange

[sumitsuri]

We had configured zimbra server and migrated some users from exchange. Now all mails are coming to zimbra only.
we would like to run zimbra in parallel with exchange for some time and when this testing is completed we will shift completely on zimbra.

for this following activities are completed:
1. we had created a ZCS Setup that is to Run in Parallel with Exchange.
2. Provisioned few users in the Mail setup on ZCS.
3. these users are migrated to ZCS and change the Attribute of those specific users to point to Zimbra, which will direct the mail flow of these users to ZCS now.

now we are willing to do some activity so that the mails for these users coming to zimbra must also be transfered to exchange for failover testing.

we got this information that it can be achieved using zimbraMailTransport Parameter for all the Users to Point to Exchange. This will make sure that all mails of all Users are routed to Exchange also.
i would like to know how and where we can configure this parameter.

[soxfan]

Well, this is kind of like the Split Domain setup described in the Zimbra Wiki here, so you may want to check it out. This page describes how to set the zimbraMailTransport. However, I'm not sure about your scenario where you want all the messages, even for the users you have migrated over to Zimbra, to go to the Exchange server. You may need to setup some type of additional forwarding for this.

[sumitsuri]

Yes we had already worked with the solution suggested by you. but it is basically a relaying option.
what i was thinking that if it is possible to sustain mails on exchange and zimbra.
that will be good enough for those persons who are currently working on exchange and willing to move on zimbra but first want to fully test it as they are new for zimbra and for those who are having organizational policies stopping them to use a software without perform full testing with failover mechanism.

[QuantumMechanic]

I work at an institution that would very much like to get away from Exchange and my CIO has asked me if I can implement a "test deployment" using a limited number of on-campus users. (This would be about 15-20 people.) However, we need to keep those 15-20 users still on the Exchange server as a backup during the testing phase. Is there any way to sync just a subset of users between the Zimbra and Exchange servers in an active way? I need to have exact copies of Calendar, Tasks, Contacts, and e-Mail (maybe even Notes) on both servers at all times. This is more of a mirrored domain rather than the split domain problem described previously. Is this a pipe dream or can it be done?