Yesterday, while working with my colleague Michael Anderson, I needed to investigate where a particular on-premises value was being synced in AAD. The result is this table:
| AD Property | Get-MsolUser | Get-AzureADUser | Get-User | Get-CSOnlineUser | |
| Friendly name | ldapDisplayName | ||||
| Telephone number | telephoneNumber | PhoneNumber | TelephoneNumber | Phone | Phone |
| Pager | pager | – | – | Pager | – |
| Mobile | mobile | MobilePhone | – | Fax | MobilePhone |
| Fax | facsimileTelephoneNumber | Fax | FacsimileTelephoneNumber | Fax | Fax |
| IP Phone | ipPhone | – | – | – | IPPhone |
| Home | homePhone | – | – | HomePhone | HomePhone |
| {otherMobile} | {AlternateMobilePhones} | – | – | – | |
| {otherIpPhone} | – | – | – | – | |
| {otherHomePhone} | – | – | {OtherHomePhone} | – | |
| {otherFacsimileTelphoneNumber} | – | – | {OtherFax} | – | |
| {otherPager} | – | – | – | – | |
| {otherTelephone} | – | – | {OtherTelephone} | {OtherTelephone} | |
It’s important to note that values displayed in braces { } are multivalued attributes, so if there’s something stored in one on-premises that you need or want to map to a a different attribute in Azure AD, you’ll need to either map it to another multivalued attribute or extract the value so you can write it to a single-valued string attribute. I have a quick guide on how to do that here: https://bhr.62e.myftpupload.com/2020/05/13/use-an-msexchextensioncustom-attribute-in-exchange-online/
Why Get-User? Different properties will show up in Get-Recipient, Get-MailUser, and Get-Mailbox. Get-User will show all of them that are forward-synced into the Exchange service.
The two AAD Connect Synchronization Rules that handle most of these flows are (default) In from AD – User Common (105) and In from AD – User Common Exchange (106):

That’s it for this round of “where is my attribute?”

