Exchange Online has grown to be an integral part of so many infrastructure email systems. Often serving as the bridge between legacy email systems and the new M365 cloud-centric architecture; Exchange Online has grown to a new way to accomplish older, customized tasks in the modern M365 or M365 hybrid enviroment.

Below is a few common problems that can occur with Exchange Online and things to try to resolve them:

1. Spam

Fixes:

• Enable Microsoft Defender Office 365 policies.
• Train users how to recognize phishing.
• Create custom transport policies to block known bad senders/domains.
• Enable report message add-in so users can flag suspicious mail.

2. Mailbox Dimensions and Quotas

Fixes:

• Enable Placed Archive Mailboxes to users who are close to quota.
• Use Auto-Expansion Archives (E5/Plan 2) if licensed.
• Teach users how to clean Outlook’s mailbox using Policy Retention, or Cleanup Tool.

3. Outlook connectivity issues

Fixes:

• Test profile corruption using Outlook/safe mode.
• Recreate Outlook’s profile.
• Check Remote Connectivity Analyzer to see if AutoDiscover is enabled.
• Cached Exchange Mode needs to be tuned (disabled in the case of large shared mailboxes).

4. Calendar Delegation and Sharing Issues

Fixes:

• Use Outlook Online (OWA), a web-based version of Outlook, to set up calendar permissions.
• Remove and readd delegate permissions when sync fails.
• Exchange Online must be used by both users (hybrid deployments cause many issues).
• Run Get-MailboxFolderPermission and Add-MailboxFolderPermission for precise control.

5. Shared mailbox and Distribution Group Problems

Fixes:

• Recheck group membership in EAC – Groups.
• Make sure AutoMappingis enabled for shared mailboxes.
• If shared mailboxes is not visible manually add via Outlook – Account Settings.
• Allow time (upto 24-hours) for changes in provisioning to sync across all services.