Download this PowerShell script –Download
This will perform a test pass for adding the new [email protected] as a secondary email address to all mailboxes. Use the log file to evaluate the outcome before you re-run with the -Commit switch.
PowerShell
.Add-SMTPAddresses.ps1 -Domain office365bootcamp.com
This will perform a test pass for adding the new [email protected] as a primary email address to all mailboxes. Use the log file to evaluate the outcome before you re-run with the -Commit switch.
PowerShell
.Add-SMTPAddresses.ps1 -Domain office365bootcamp.com -MakePrimary
This will add the new [email protected] as a primary email address to all mailboxes.
PowerShell
.Add-SMTPAddresses.ps1 -Domain office365bootcamp.com -MakePrimary -Commit
Source : https://gallery.technet.microsoft.com/office/Bulk-Add-SMTP-Addresses-to-e3d28842