A former employee's account is disabled in Active Directory and the mailbox has been converted to a shared mailbox. I'm trying to configure an automatic reply through the Exchange admin center and Exchange Online PowerShell, but both return "Object reference not set to an instance of an object." The mailbox folders are below quota, and the original user still exists in Active Directory and Entra ID. Has anyone encountered this error or found a reliable way to configure the automatic reply?
3 Answers
Check for duplicate accounts or objects with the same alias, mail nickname, or another identifying attribute. An identity collision can cause the admin center and PowerShell commands to resolve the wrong object. Try targeting the mailbox with a different unique identity, such as its full SMTP address or distinguished name, rather than relying on the display name or alias.
If a true out-of-office response is not required, a mail flow rule can provide a similar response for messages sent to the retired employee’s address. It may be easier to manage, but be careful with sender scope, internal versus external messages, and avoiding mail loops.
Try converting the shared mailbox back to a regular user mailbox and test the automatic reply there. If that still fails, temporarily enable the account and assign it as the mailbox user. Afterward, you can convert it back to a shared mailbox. That quick test may be easier than troubleshooting a problem that only affects this one mailbox.
I converted it back to a user mailbox, but the same error appeared. I may have to re-enable the account and configure it while signed in as the user, although I was hoping to avoid that extra process.