I am facing a problem when a migration process from GSuite led to an unconsistent user's mailbox - migration process stopped several times and finally hit mailbox size limit (100Gb) which is much more than expected (~65Gb).

So the mailbox should be cleaned completely and I would like to perform another kind of migration (not API-based, at least - via IMAP or even PST). The problem is I can't find any solution to empty the mailbox.

What I have tried so far:

  1. Emptying the mailbox with outlook online - folders are empty, but mailbox usage is about 70Gb (this is probably my mistake - see below)
  2. Empty the mailbox using search-mailbox -DelectContent cmdlet - extremely slow, no effect, mailbox usage is about 70Gb
  3. Applying set-mailbox -RetainDeletedItemsFor 0 cmdlet - still no effect.

Is there a way like it was in on-prem exchange - disconnecting a mailbox from user and creating a new one from scratch?

2 Answers 2


In Office 365 admin center > USESRS > Active Users > find the user, delete it. It will go to the Deleted Users.

Create a brand new mailbox with exactly the same information for the user

In addition, i found a similar thread for your reference: Wipe Content from an Exchange Online Mailbox

  • Is this method effective?
    – Joy Zhang
    Aug 10, 2020 at 7:01
  • Sorry for the late reply but - method with delete/create users won't work - script from the article did the trick but I can't say it is really simple. I mean I experience no problems with powershell but the script generates eceptions, leaves mailbox unerased etc. Anyway, again, it did the trick. Thank you.
    – Cyrill U
    Sep 1, 2020 at 15:23

Here's one method of doing it:

Remove the Exchange Online license from the user in question.

Connect to Exchange Online with Powershell.

Run the following command:

Set-User youruser@yourdomain.com -PermanentlyClearPreviousMailboxInfo

Re-assign the Exchange Online license.

This will create a new, empty mailbox for the user in question.

  • Seems it isn't working. I removed licenses and ran the command, it did withiut errors. Now, when I add licenses back, I get the same size of mailboxes :(
    – Cyrill U
    Aug 5, 2020 at 9:10

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