Alias emails in O365 with hybird on-prem AD sync
If you use O365 in hybird mode, with your tenant sync-ed to your on-prem AD or Exchange server, then you will definitely run into an issue if you try to add an alias email address to a user.
When you attempt to add an alias, or alternate, email in your Exchange Admin Center portal you will see this error message.
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To get around this you’ll need to edit the user “local” from your on-prem AD. In AD, right-click and open the users’ properties. Select the tab “Attribute Editor”
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You will want to look for and edit the following two attributes.
- msExchShadowProxyAddresses
- ProxyAddresses
Add the user’s alias/alternate email address into the above mentioned attributes in the form of: smtp:updatedname@domain.tld
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That’s it. Now you just need to let your AD sync back up to the O365 cloud.
WARNING: If you add it in CAPS (SMTP:updatedname@domain.tld) then it will get interpreted as the default address and not as an alias/alternate email. Make sure that “smtp” is lowercase.