Exchange Server 2019 Mailbox Database Error and Definitive Fix Guide

This guide explains how to resolve the Exchange Server 2019 mailbox database error
that appears as “Mailbox Database Temporarily Unavailable”.
The issue prevents users from accessing Outlook Web Access (OWA) and mailbox services,
even though Exchange services may appear to be running normally.

The steps below are verified specifically for Microsoft Exchange Server 2019,
but the same logic also applies to Exchange Server 2016 environments.

Symptoms

• OWA not opening
• Mailbox access failure
• Exchange services running but users disconnected
• Database mount errors
• MailboxOfflineException messages

Microsoft.Exchange.Data.Storage.MailboxOfflineException
Microsoft.Mapi.MapiExceptionMdbOffline
The mailbox database is temporarily unavailable
Cannot open mailbox Microsoft System Attendant

Root Cause in Exchange Server 2019

In Exchange Server 2019, internal system mailboxes depend directly on a mounted mailbox database.
If a database enters Dirty Shutdown state, Exchange blocks mounting
to protect mailbox consistency.

Get-MailboxDatabase -Status

Name                        Mounted
Mailbox Database Standard   True
Mailbox Database Unlimited  False

Why OWA Stops Working

Exchange Server 2019 requires system mailboxes such as:

• Microsoft System Attendant
• Arbitration Mailboxes
• Migration Mailboxes

If the database is offline, these mailboxes cannot initialize,
causing OWA and internal Exchange components to fail.

Main Reason: Dirty Shutdown

Dirty Shutdown occurs when Exchange Server 2019 stops unexpectedly before committing
all transactions to the database.

• Unexpected reboot
• Power outage
• Storage latency
• Backup interruption
• Disk I/O timeout

Check Database State

eseutil /mh "D:\DBASE\Mailbox Database\Mailbox Database.edb"

If the result shows:

State: Dirty Shutdown

The database must be recovered before mounting.

Definitive Solution — Soft Recovery (Exchange 2019)

Step 1 — Identify Paths

Get-MailboxDatabase "Mailbox Database" | fl EdbFilePath,LogFolderPath

Step 2 — Run Soft Recovery

eseutil /r E00 /l "D:\TLOG\Mailbox Database" /d "D:\DBASE\Mailbox Database"

Expected output:

Operation completed successfully

Step 3 — Verify Clean Shutdown

eseutil /mh "D:\DBASE\Mailbox Database\Mailbox Database.edb"

State: Clean Shutdown

Step 4 — Mount Database

Mount-Database "Mailbox Database"

Expected Result

• OWA operational again
• Mailbox access restored
• Exchange Server 2019 services normalized
• System Attendant errors resolved

Post-Recovery Checks

chkdsk D: /scan

• Check MSExchangeIS logs
• Review ESE events
• Verify storage health

Best Practices for Exchange Server 2019

• Use Exchange-aware backup software
• Exclude database/log folders from antivirus
• Monitor disk latency
• Avoid forced shutdowns
• Maintain storage health monitoring

Quick Summary

Conclusion

The Exchange Server 2019 mailbox database error may appear critical,
but in most cases it can be resolved safely using soft recovery.
Always attempt log replay before performing database repair operations.