Exchange Online Mail Enabled Users redirecting to eternal SMTP

New Contributor

Hi all,

I have a client that has been using Ex2010 and has used mail contacts object to effectively build a reverse DL. They have say 30 Unique contacts with a proxy address inside their Org, but use the External Email Address field to send to the same SMTP.

For example, a user contact called Bill Smith with an internal address of but the external address of

They then have Jane Doe with an internal address of but the external address of


So essentially the GAL allows staff to find Bill or Jane and send to them but it goes to a single external mailbox.


Exchange Online will not allow this bad behaviour for obvious reasons but I notice there is an Attribute in MailEnabled Users for "ForwardingAddress" that I can't use or write to. Does anybody know if ;

a) Can I write an external address to this attribute to replace the above behaviour or

b) a way to accomplish the same?


I know I can write a transport rule that redirects from contact Jane Doe with an internal address of to a Contact object of but this is not only messy for the number involved, but will it not also potentially cause issues with SPAM detection engines?


If there are any ideas, I would love to hear them.


2 Replies
Best Response confirmed by Ian_Culliver (New Contributor)

Exchange Online does not enforce uniqueness of the ExternalEmailAddress property, so you should have no trouble doing this:


[10:23:47]# Get-MailUser MU* | ft Name,Primary*,Externa*
Name PrimarySmtpAddress           ExternalEmailAddress
---- ------------------           --------------------
Just make sure you create them with different PrimarySMTPaddresses (use the relevant parameter for new-mailuser).

@Vasil Michev Thanks you so much Vasil, This works perfectly well as long as you stay away from the GUI and force the PrimarySMTP as you said. I was missing that step.