LEGACY: The instruction below with the steps to create a Mailbox Search is no longer relevant and has been deprecated by Microsoft. Go to this post for an updated version on how to perform this via the Microsoft Security and Compliance Center:
https://ex-shell.com/2020/11/11/exchange-online-place-a-hold-on-a-soft-deleted-mailbox/
Scenario: A person is no longer with the organization and their mailbox is currently retained in Exchange Online as a Soft-Deleted mailbox (get-mailbox -softdeletedmailbox). It was discovered that we need to place the mailbox on a hold to keep the email data preserved.
Scriptlets:
We are going to create a InPlace Hold on the inactive mailbox by running the following commands:
$mbx = get-mailbox -identity <user> -softdeletedmailbox
New-MailboxSearch -Name “InactiveMailboxHold” -SourceMailboxes $mbx.DistinguishedName -InPlaceHoldEnabled $true
Ex-Shell 