Exchange Online Archive enabled but Managed Folder Assistant not moving any mail

[u/dark_mercurial3366]

Got a bit of a weird Exchange Online archiving issue and wondering if anyone has seen similar. This is a hybrid Exchange environment with on-prem AD/Exchange and the mailbox hosted in Exchange Online.
 
User has a pretty large primary mailbox around 85GB and Online Archive is enabled, but the archive is basically empty.
 
Things I've checked:
 
ArchiveStatus = Active
 
Default MRM Policy assigned
 
Default 2 year move to archive enabled
 
RetentionAction = MoveToArchive
 
AgeLimitForRetention = 730 days
 
RetentionHoldEnabled = False
 
ElcProcessingDisabled = False
 
No obvious holds
 
No folder-level archive policy overrides
 
I pulled the mailbox diagnostics as well. MFA/ELC seems to be running successfully, but the latest run shows:
 
ElcLastRunArchivedFromRootItemCount = 0
 
ElcLastRunTaggedWithArchiveItemCount = 0
 
For comparison, I checked another mailbox in the same tenant using the exact same Default MRM Policy. MFA is actively moving eligible items into that user's Online Archive, so the policy itself seems to be working.
 
Manual moves from the affected mailbox into Online Archive also work fine.
 
It looks like MFA is processing the affected mailbox but, for whatever reason, isn't finding anything eligible for the 2-year archive rule.
 
Anyone come across this before?
 
Is there anything else worth checking to understand why the items aren't being considered eligible?

[u/pointar]

Try a start-managedfolderassistant -identity mailboxupn -fullcrawl and see if the items archive for one of the users

[u/7amitsingh7]

A likely cause is the retention tags. MFA is running, but it isn't finding items that meet the 2-year archive criteria. Check folder-level or personal retention tags, message age/metadata, and migration history. If you're also dealing with a large archive in a hybrid environment, this guide on migrating large archive mailboxes to Microsoft 365 may help.

[u/auditvault-de]

You've already ruled out the usual causes (policy assigned, MoveToArchive DPT, no holds, ElcProcessingDisabled=False) — with an 85 GB primary, the most likely answer is throttling: the Managed Folder Assistant in Exchange Online is throttle-based and processes large mailboxes very slowly; Microsoft documents this throttling as unavoidable for large mailboxes. Archive moves then happen in small batches over days, not in one run.

To confirm it's healthy-but-slow, not stuck:

powershell Export-MailboxDiagnosticLogs <mailbox> -ComponentName MRM

Any MRM errors will be in that log; "no logs were found" means the mailbox was processed without errors — i.e. it's just working through the backlog. Also run the "Run Tests: Retention Policy" diagnostic (M365 admin center, documented on the retention tags/policies page). Note you can't hand-trigger the assistant against EXO from the REST-based module (v3) — Start-ManagedFolderAssistant isn't exposed there; the throttle cycle is the supported path.

[u/Shnicketyshnick]

Edit: It appears I remembered wrong. Ignore me. Was the 2 year policy put on the mailbox less than 2 years ago? It starts counting from that point, won't flag things older than that immediately

[u/EscapeArtist112 → u/Shnicketyshnick]

I’m pretty sure this only applies to the Deleted Items folder. All the other default folders should retroactively tag the dates on the messages for when they were received.

[u/saltyslugga]

Check a few actual items older than 730 days and inspect their PolicyTag, RetentionDate, and RetentionFlags MAPI properties. Stale or explicit item-level tags can override the folder and default policy even when no folder override is visible.

If those properties look wrong, clear the item-level tags and run MFA with -FullCrawl.