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Setup new Office 365 mailbox user Active Directory DirSync without Exchange Server On-Prem


Before Server 2008R2, it used to be a pain to edit exchange mail attributes for users without using an exchange server in your environment. ADSI-edit and PowerShell were two tools you could use, but thankfully that has changed since 2012 provides easy access to the Advanced attributes right from the Properties of the user in Active Directory (AD). This how-to assumes you have no on-prem exchange servers anymore and you have DirSync setup properly with all your email users in Office 365.

Quick instructions for setting up a new Office 365 mailbox user in AD:

  • Create the User (in AD)
  • Right-click and go to Properties.
    On the General Tab: Make sure the user’s email address is correct
    On the Account Tab: Make sure the User Logon Name is the first part of their email address (for example first initial +last name). Then make sure the domain is correct. You want the domain to be their email address domain, not that of the local AD domain name if they are different. Then make sure User Logon Name for Pre Windows 2000 is the same as the other logon name, or as close to it as you can be while being unique within the organization.
  • Set the Email Address Properties
  • Click on Attribute Editor tab. Click on Filter and make sure you can see all attributes, not just those with values.
  • Look for these properties and update the values accordingly:
    proxyAddresses: SMTP:primary.email@domain for this user – SMTP needs to be in capitals. This is also where you would enter in any email aliases, just make sure they start with lowercase smtp:
    targetAddress: SMTP:first_part_of_email@tennantname.onmicrosoft.com
    NOTE: Both addresses need to be unique (within your directory). Attribute Editor will let you enter the same for both, but if you do then the user won’t properly replicate to Office 365 when the Directory Sync (DirSync) runs.
  • Speaking of Directory Sync, aka Azure AD Connect, you can wait for it to run (30min max for a directory sync…password hashes sync every 2min) or you can force it to sync: Force Dir Sync in Azure AD Connect | IT by Mitch (mitchellenright.com)
  • Don’t forget to License the User for Exchange Online in Office 365. Their mailbox should be created soon after you do so and you’re all set.

Other Attributes:


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