What Is Mailnickname?
mailNickName: An Email Aalias
mailNickName is an email alias. You could open up Active Directory Users and Computers by logging into your domain controller and finding the user that owns the mailbox, then selecting Properties.
Exchange Mail Address Policy
mailNickName is an email address. If you are using Exchange, you need to change the mail address policy to keep up with the mail attribute. You can specify additional formats or domains for each user if you use the policy.
The MailNickName Attribute Value
The UPN is used to sign-in. The UPN that a user can use depends on whether or not the domain has been verified. If the domain has been verified, a user with that suffix will be allowed to sign-in to the cloud.
No additional steps are needed to enable alternate login ID with azure AD. The alternate ID can be configured from the wizard. Under the section sync, you can see the sign-in configuration for your users.
The attribute for alternate login ID can be found under the User Principal Name drop-down. The value of the UserPrincipalName attribute is set to MOERA, so it is important to understand how the value is calculated. The MailNickName attribute value is only updated when there is an update to the on-premises mailNickName attribute value.
Thumbnail Photo and LDAP Attributes
The x500 standard had a draft that listed both jpeg Photo and Thumbnail Photo, and the suggested format was jpeg. The thumbnail photo attribute is the correct field to use in the collection of Outlook LDAP attributes. A string is stored as a Thumbnail Photo. If you want to use it, you need to establish whether or not it is populated with something or you can see Octet.
On the Protection of Duplicate MailNicknames in Office365 Group Replication
Office365 groups that have duplicate mailNicknames will not be affected. If a user attempts to modify the mailNickname property through a method other than PowerShell, the service will check the new mailNickname to see if it is unique. The modification will be rejected if not.
The msExchHideFromAddressList attribute did not copy into mailboxeS
The msExchHideFromAddressLists attribute was fine to AAD, but it did not copy into mailboxes because the user was no longer connected to the mailbox.