Script to add legacyexchangedn as x500 alias into AD user object for Exchange Online

If a scenario existed whereby there was a non exchange hybrid like lotus notes or group wise messaging platform and some users were using Office365 and co-existence was achieved by uploading all of the onpremise users' as external contacts. Office365 users recipients have messages forwarded to from the source messaging platform. 

As you begin to convert the onpremise users' to federated or managed users. You need to capture that user's legacyexchangedn and ingest it into the users' AD users' proxyaddresses attribute as an x500 alias to prevent potential NDRs from existing Office365 users.

So run this Exchange Online command

get-mailcontact - resultsize unlimited | select-object legacyexchangedn,primarysmtpaddress | export-csv "csv file path" delete the first line 1 from the output of the csv

Then download this SCRIPT and edit the following lines

• edit line 11 and enter your domain name
• edit line 25 and enter your domain name

Then hold down shift and right click on the csv and select copy as path and paste the path into the window as per the image below and press the green play button.

This script will then search the root of the domain based on the domain name and mailnickname and add an x500 alias into the users' proxyaddresses attribute which will then be synced to Office365 via dirsync

So before the OU containing the AD user objects that needs to be synced you will need to run this command as there will be conflicts in dirsync.

import-csv "C:\Users\admin\Desktop\contacts to be deleted\contacts.csv" | Foreach-Object{Get-Mailcontact $_.primarysmtpaddress | remove-mailcontact -Confirm:$false}

Credit : Eduardo Martin