In this article, we will learn how to fix the mailbox server cannot be removed from the DAG (Database Availability Group). You want to remove a mailbox server from the Database Availability Group (DAG). Nevertheless, when performing the removal process, you get the error message “Mailbox server cannot be removed” from the “Database Availability Group” because the mailbox database has multiple copies. Use “Remove-MailboxDatabaseCopy” either to remove the copy (database) from this server or to delete the copies from other servers in the database availability group (DAG). Why is this happening, and what is the resolution to remove the mailbox server from the DAG? Visit Microsoft to learn more about how to remove the database availability group server.
Table of Contents
“Mailbox server cannot be removed” from Database Availability Group

Use the Exchange admin center to remove a mailbox database copy
In the Exchange admin center, go to the Servers option and then click on the Databases tab.
Click on the mailbox database whose copy you want to remove.
On the left side, in the Details pane, go to the passive copy you need to remove, and then click Remove.

A warning dialog box will open; click on the yes button to confirm the removal.

Select the OK button to confirm the removal after reviewing any messages.

You can manually delete any “database and transaction log files” from the database group membership server from which the database copy is being removed.
Click on the database availability group tab, highlight your DAG, and then click on the edit button.

Select the server you want to remove from the member servers, and then click on the – icon. Click save.

Conclusion:
This article teaches you how to remove a mailbox server from the DAG configuration in Exchange Server 2019. It’s necessary to remove the mailbox database copies before removing the member server from the database availability group. If you don’t perform this first, an error message shows up saying that the “mailbox server cannot be removed” from the Database Availability Group.