Thank you for the the link Pat, much appreciated.
It looks like there is no elegant solution to this.
The users in domain abc.com are transferring to def.com.
def.com and associated mailboxes are hosted by a seperate company.
The users are sending from the existing abc.com infrastructure and all replies should be routed into the new def.com infrastructure.
The replies are subsequently routed back to abc.com via the targetaddress AD property / alternate recipient.
There is no requirement to be selective for the senders address.
When the users physically transfer to def.com the targetaddress / alternate recipient will be removed from the def.com mailbox, mail will be delivered locally and they can continue to work as normal.
The best solution in the linked post might well be using a pop3 client where the reply address is usually a free text field.
One idea I've just had;
Use recipient policy to set a new primary smtp address of def.com for each user in the abc.com environment.
When they send externally, the reply address will be def.com.
They will still be able to receive mail on their abc.com address as it would now be a secondary smtp address and the environment is configured to route mail inbound for that domain.
Possible downside - if anyone sends internally to a def.com address it will resolve to an internal recipient and not be sent outbound...
Although that shouldn't be a problem we are currently diverting mail back to that environment anyway - so the outcome is the same...
(might be missing some finer points here).
Regards
Simon J Cook
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