Primary Mailbox to Online archive

Question

A primary mailbox folder is not auto deleting after moving that folder to the online archive. It is also a auto expanding online archive. I'm trying to find the source that say that this does this cause it is a safety feature

Answer 1

Dear LM,

Good day, and thank you for reaching out to the Q&A Forum. If I understand correctly, after messages are moved into the Online Archive, the corresponding empty folder remains in the primary mailbox, and you are looking for Microsoft documentation confirming whether that behavior is intentional.

The short answer is yes, this is expected behavior, though it is not documented as a "safety feature" as such. Exchange Online's Move to Archive retention action operates on mailbox items, not on folders. Microsoft's documentation is consistent on this point: retention tags apply retention settings to individual messages, and when a message reaches its retention age, it is either moved to the archive mailbox or deleted. The Managed Folder Assistant inspects items in the mailbox, stamps those subject to retention, and then takes the specified retention action on items past their retention age.

There is no mechanism in MRM that deletes the source folder afterwards. The empty folder therefore remains in the primary mailbox even after all eligible content has moved to the matching folder structure in the archive. If the folder is no longer needed, it has to be removed manually by the user or an administrator.

On the "safety feature" framing, I was not able to find any Microsoft article that describes the retained empty folder as a safety feature. The more supportable explanation is simply this: MRM archive policies act on mailbox items, not on user-created folders. An empty folder may therefore remain in the primary mailbox once its eligible items have been moved to the Online Archive.

It is also worth noting that Microsoft explicitly states you cannot create a Retention Policy Tag (RPT) to move messages to the archive, and that RPTs only support delete actions. Archiving is handled through Default Policy Tags or Personal Tags, which again act at the item level rather than the folder level.

Auto-expanding archiving governs archive storage capacity and provisioning. It does not alter the MRM retention action from item processing into folder deletion, so enabling it will not cause Exchange to remove empty source folders from the primary mailbox.

For reference: 

Customize an archive and deletion policy (MRM) for mailboxes | Microsoft Learn

Default folders that support Retention Policy Tags in Exchange Online | Microsoft Learn

I hope this information helps clarify the situation and provides you with a clear path forward. Should you have any further questions or need additional assistance, please don't hesitate to reach out. I'm always happy to help. Have a wonderful day! 

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