Currently I am working with an environment that looks like this:

Smaller organization using Google Apps for e-mail, let's say this domain is @gapps-example.com

Larger organization using MS Exchange for e-mail, let's say this domain is @msexchange-example.com.

There is now a need to give users at the smaller organization AD accounts in the larger organization. Users should show up in the Exchange GAL with their primary e-mail address on record being their @gapps-example.com e-mail address. This alone would be easily doable using Exchange "Mail Users".

The hard part is that we also want to have a hidden / secondary "alias" e-mail address @msexchange-example.com that would auto-forward to their normal GApps @gapps-example.com e-mail address, for each user from the smaller organization.

This would be for odd cases where someone needs to verify their employment at the larger organization by getting a verification e-mail sent to them at an @msexchange-example.com e-mail address.

Does anyone have any advice on how to technically achieve something like this with Exchange?


  • Well I think the secondary Alias email is not an issue here as Exchange already allows you to have multiple SMTP addresses for users but only one of those emails can be the primary SMTP address. If you want to forward the email from exchange then the users will need an inbox or a distribution list or something to work. – Junaid Oct 13 '16 at 23:17
  • As far as I know (feel free to correct me if I am wrong) you can only have multiple SMTP addresses for an Exchange Mailbox, not for a "Mail User" (which is essentially just a Mail Contact that's an actual AD user also). – Aaron L. Oct 13 '16 at 23:58

This is exactly what a Mail Contact in Exchange does. The Primary SMTP address for the object is for an external domain, but there is a default alias for the internal Exchange domain, which would pass your requirement.

Mail Contact:

  • No AD account, just an Exchange object which has an alias in the Exchange domain.
  • Primary email address (as well as the one shown in the GAL) is for the external domain.

Mail User:

  • Has an AD account, and the primary SMTP address is shown in the Exchange domain.
  • Exchange attribute ExternalEmailAddress is set to the external mail domain.
  • Not exactly. A mail contact is a non-user object that shows up in the GAL with an external e-mail address. I could create a normal Exchange user with an @ msexchange-example.com mailbox, then create a new contact object for that user's @ gapps-example.com e-mail address, and then configure the user's mailbox to forward to the contact object, however that would still have the user's primary e-mail in the GAL show up as their @ mxexchange-example.com address. – Aaron L. Oct 13 '16 at 23:54
  • I guess I glossed over the 4th paragraph. You are actually looking for a Mail User, which does have an AD account and shows the Exchange domain as the primary email address. – blaughw Oct 13 '16 at 23:58
  • I do not believe you will be able to set the primarySMTPAddress attribute for an external domain on a Mail User. – blaughw Oct 14 '16 at 0:00
  • A Mail User wouldn't show the Exchange domain as the primary e-mail address, since a Mail User is just like a Mail Contact, except that it is an actual AD user as well. Mail Users, just like Mail Contacts, have an external e-mail address. As far as I know (and please correct me if I am wrong) any solution involving an actual, functional e-mail address at the Exchange domain name would involve creating a mailbox of some sort. – Aaron L. Oct 14 '16 at 0:01
  • 1
    I have a bunch of Mail Users, pending an acquisition to go-live. Primary SMTP is my exchange domain, and the exchange attribute ExternalEmailAddress is configured for the remote mail domain (which does happen to be on GApps.) – blaughw Oct 14 '16 at 0:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.