Forum Discussion

mOrbo-ms's avatar
mOrbo-ms
Copper Contributor
Mar 08, 2026

Mail retention - storage of potential duplicate Data

Hi,

 

We are planing to implement retention policies in Microsoft Purview. 

My question is, where and how often are the files stored? The question is about storage space.

 

For example:

A User has a Mailboxsize of 20 GB.

The retention policy is: "Retain Mails for 5 years, don't delete after".

And another (legacy) policy: "Move Mails to online archive after 1 year".

 

Lets say he now has a full Mailbox with his 20GB. After activation of the online archive and the retention policies, his data gets moved.

10GB are older than one year, so they will move to the online archive.

Is this move recognized by the retention policy "Retain Mails for 5 years, don't delete after"? Or does this move count as deleting and the 10GB will remain in the hidden "recoverable items" folder of his primary mailbox?

 

For the rest of the Mails:

If he is moving 5GB to a M365 Group Folder and 5GB to a Public Folder, are these moves recognized by the retention policy "Retain Mails for 5 years, don't delete after"? Same question as above, does this move count as deleting and the 10GB will remain in the hidden "recoverable items" folder of his primary mailbox?

 

If all moves are recognized by the system and the Mails are only stored once (probably with a reference to the old folder/mailbox), the used spaces should look like this:

Primary Mailbox: 0 GB

Online Archive: 10GB

M365 Group: 5GB

Public Folder: 5GB

 

If the Mails are stored multiple times in the hidden "recoverable items folder", it should look like this:

Primary Mailbox: Hidden 20 GB (Mailbox is still full)

Online Archive: 10GB

M365 Group: 5GB

Public Folder: 5GB

 

What is the case here?

 

Thanks.

microsoft purview

2 Replies

  • mOrbo-ms's avatar
    mOrbo-ms
    Copper Contributor
    Mar 09, 2026

    Thanks for you Answer. But my question is more about the Mailboxsize itself, rather then deleting items.

    We force our users to sort their mails into PublicFolders or Groups. We do this by a strickt limited Mailboxsize. Mail retention (as required by law) is done by Journaling right now. 

    If we move to the retention policies in Microsoft Purview and all the items stay in the Mailboxes, even if they are moved to PublicFolders or M365 Groups, the Mailbox will grow and grow, until the retention policy allows deleting (this is after 10 years for some mails). 

    Also, an associated online archive is actually a second mailbox, archiving would not free up any space in the primary mailbox. This would mean, that the Microsoft Purview retention policies are not a equal replacement for Journaling Mailboxes.

  • VasilMichev's avatar
    VasilMichev
    MVP
    Mar 09, 2026

    There are no files, everything is stored in place, within the mailbox itself. Moving items within the mailbox itself, including to/from any associated archive, does not affect storage. Moving data between mailboxes, or to Groups/Public folders will result in a copy of any moved item being preserved for the duration of the matching retention policy.

    In other words, if the mailbox is under (generic/blanket) retention policy, all data within is preserved, regardless of any deletions/moves. This is why "cleanup" operations require you to (temporary) disable the retention policy, see for example https://learn.microsoft.com/en-us/exchange/policy-and-compliance/recoverable-items-folder/clean-up-deleted-items 

    Nowadays, we do have the Priority cleanup feature as well, which can help in such scenarios.