Create MRM Retention Tags
Open Microsoft Purview and navigate to the MRM Retention tags tab.
Create a new tag.
Give the tag a meaningful name, provide a brief description of what the tag is for and then click next.
Select “Automatically to entire mailbox” then click next.
Define the retention period and action. In this example, we want to move all email objects older than 6 months into the users online archive. Click next when definitions are set.
Review the tag settings and click on submit.
Create Retention Policy
In Purview, navigate to the MRM Retention policies tab, and click on “New Policy”.
Give your policy a meaningful name, and click on “Add tag”.
Select all retention tags, except those referring to the archiving time frame that you don’t want to apply.
In our example, we only want 6 month archiving to occur, so we’ll deselect the 1 and 2 year options.
Review the selected tags and click next.
Review the policy and click submit.
Apply Custom Policy
Open the Exchange Admin Center, select the mailbox you wish to apply the policy to, click on the Mailbox tab, then click on “Manage mailbox policies”.
Click on the Retention policy drop-down, select your newly created MRM policy, then click Save.
Don’t forget that you’ll need to force this process to run immediately via PowerShell if primary mailbox space is urgently required; the process for performing the PowerShell forced archive are attached to this article in the related items section.