0x80040200 – Invalid Mailbox Resolution Guide

1.Verify Mailbox Existence

Use Exchange Admin Center (EAC) or PowerShell:

Get-Mailbox -Identity user@example.com

Confirm the mailbox is active and not in a disconnected or soft-deleted state.

2.Recreate Mail Profile

1. Go to Control Panel → Mail → Show Profiles.
2. Delete the corrupted profile and create a new one with correct credentials.

3.Flush DNS and Autodiscover Cache

1. Run in Command Prompt (Admin):
2. ipconfig /flushdns
3. Delete Outlook Autodiscover cache from:
4. %LOCALAPPDATA%\Microsoft\Outlook\RoamCache

4.Check AD and Exchange Replication

1. Ensure that all domain controllers and Exchange servers are fully synced.
2. Use: repadmin /replsummary and Get-ExchangeServer | Test-ServiceHealth

5.Review Mailbox Permissions

1. Ensure the user or service account has appropriate Full Access or Send As rights.

 Optional Step (If Applicable)

• If the mailbox was recently migrated, ensure Outlook is connecting to the correct Exchange version or Office 365 endpoint.

Run Outlook in Safe Mode:

1. Outlook.exe /safe