Adding and Removing Extensionattribute to Ad Object

I used the following today - It works!

Add a value to an extensionAttribute

 $ThisUser = Get-ADUser -Identity $User -Properties extensionAttribute1
    Set-ADUser –Identity $ThisUser -add @{"extensionattribute1"="MyString"}

Remove a value from an extensionAttribute

  $ThisUser = Get-ADUser -Identity $User -Properties extensionAttribute1
  Set-ADUser –Identity $ThisUser -Clear "extensionattribute1" 

I have struggled a long time to modify the extension attributes in our domain. Then I wrote a powershell script and created an editor with a GUI to set and remove extAttributes from an account.

If you like, you can take a look at it at

I'm sorry, that the description in the text is in German. The GUI itself is in English.

I use this script on a regular basis in our domain and it never deleted anything or did any other harm. I provide no guarantee, that this script works as expected in your domain. But as I provide the source, you can (and should) have a look at it, before you run it.

Extension attributes are added by Exchange. According to this Technet article something like this should work:

Set-Mailbox -Identity "anyUser" -ExtensionCustomAttribute4 @{Remove="myString"}

Set-ADUser -Identity anyUser -Replace @{extensionAttribute4="myString"}

This is also usefull

Or the -Remove parameter

Set-ADUser -Identity anyUser -Remove @{extensionAttribute4="myString"}

To clear the value you can always reset it to $Null. For example:

Set-Mailbox -Identity "username" -CustomAttribute1 $Null