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MSExchange ActiveSync 1023 warning

You are getting the Event ID 1023 MSExchange ActiveSync warning in the Event Viewer on the Exchange Server. The Event ID 1023 warning is showing: Exchange ActiveSync tried to access a mailbox on Mailbox server. It could not access the mailbox because the Mailbox server is offline. In this article, we will look at why it’s happening and the solution to MSExchange ActiveSync Warning 1023.

MSExchange ActiveSync 1023 warning in Event Viewer

System Center Operations Manager (SCOM) or another monitoring system is sending alerts, and you like to know what is happening. Let’s have a look at the system.

Log into Exchange Server and start Event Viewer. Expand Windows Logs and click Application. You will see the Event 1023 MSExchange ActiveSync warnings.

MSExchange ActiveSync 1023 warning event log exchange activesync tried to access a mailbox

The solution to MSExchange ActiveSync 1023

Run Exchange Management Shell as administrator. Make use of the Get-MailboxDatabase cmdlet. Read the article Get Exchange mailbox database mount status with PowerShell, if you want to learn more.

Mailbox Database DB05 is not mounted. The mounted status is showing False. Mount the database and verify the database status.

We are going to find all the mailboxes in the database that we mounted.

The next step is moving the mailbox to another database with PowerShell. We are going to move the user to the database DB01.

Check the move status and if it’s completed.

The move request completed successfully. Check if there are mailboxes in the database.

There is no output shown because there are no mailboxes in the database. Dismount the database and verify if the database is dismounted.

The database is dismounted. Now that there are no users in the database, you will not get the events anymore: Event ID 1023 MSExchange ActiveSync warning. Exchange ActiveSync tried to access a mailbox on Mailbox server. It could not access the mailbox because the Mailbox server is offline.

Read more: MSExchange Mailbox Replication 1006 warning »


To sum it up, you learned why the MSExchange ActiveSync 1023 warning shows up. You also learned the solution to it. Before dismounting the database, make sure to move all the mailboxes to another database. It’s good that Exchange Server is giving a warning in the Event Viewer.

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ALI TAJRAN is a passionate IT Architect, IT Consultant, and Microsoft Certified Trainer. He started Information Technology at a very young age, and his goal is to teach and inspire others. Connect with ALI TAJRAN on social media. Read more »

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