How to Add an SMTP address in Office365 with DirSync & ADFS enabled | JulianBen.com

If you are synchronizing an Office 365 account with an on-premises Active Directory, you know that you cannot edit exchange user properties using the Office 365 administrator portal.  In this article, I will show you how to add e-mail aliases using the Active Directory Service Interfaces Editor (adsiedit).

1. Go to Start > Run and type adsiedit.msc
2. Now, find the unit where your AD user’s reside
3. Right click the user you want to edit and click Properties.
4. Find the variable proxyAddresses – this is the one you want to edit.
   When you add new e-mail aliases, you want to make sure that your primary e-mail address will start with upper-case SMTP. Your aliases, aka, secondary addresses should be lower-case smtp.For example, I want my primary e-mail address to be firstnamelastname@example.com
   In the proxyAddresses attribute, I would put:
   SMTP:firstnamelastname@example.com
   As my alias, I want firstname.lastname@example.com… to do this, I will use lower case smtp:
   smtp:firstname.lastname@example.com

Apply the new settings and wait for your active directory to be synchronised with Office 365 (by default this happens every 3 hours)