Adding an alias for office365 user(s) Synchronized using ADSync

[somaji]

I am trying to add an alias for users synchronized with AD using ADSync. Adding SMTP and smtp in ProxyAddress attribute is not working; receiving Sync errors (removed automatically).

Any assistance would be helpful.

[#2]

What does the error say exactly? If the alias is already configured on another object in the cloud, you will receive a duplicate attribute error.
You can try adding the alias directly on the cloud object via the following cmdlet:

Set-Mailbox email address removed for privacy reasons -WindowsEmailAddress email address removed for privacy reasons

This will add the email address removed for privacy reasons alias to the mailbox, while preserving the old one as secondary.

[#3]

@somaji 

Take a look at this:

https://learn.microsoft.com/en-us/microsoft-365/enterprise/fix-problems-with-directory-synchronizati...