Permanently delete 90 days old email from deleted folder

Another option might be to use Classic Outlook AutoArchive.

Automatically Cleanup Outlook's Deleted Item and Junk Email Folders
https://www.slipstick.com/outlook/config/how-to-automatically-empty-outlooks-deleted-item-folder/

General info on AutoArchive

https://support.microsoft.com/en-us/office/archive-older-items-automatically-25f44f07-9b80-4107-841c-41dc38296667

https://support.microsoft.com/en-us/office/autoarchive-settings-explained-444bd6aa-06d0-4d8f-9d84-903163439114

Use one of the solutions outlined in this article (note you might need support from an admin, if no relevant tags/policies exist in your tenant): https://michev.info/blog/post/5868/make-sure-deleted-items-are-automatically-removed-from-microsoft-365-mailboxes

In Classic Outlook for Windows connected to Exchange, this behavior is controlled by server‑side retention/deleted item settings, not by a client rule.

Key points from the Exchange side:

• When items are deleted from any folder, they go to Deleted Items.
• When items are deleted from Deleted Items (or deleted with Shift+Delete), they are permanently deleted from the user’s view and moved into the Deletions subfolder of the Recoverable Items folder.
• Items stay in Recoverable Items → Deletions until the deleted item retention period expires. The default is 14 days, but it can be changed per mailbox database or per mailbox.
• After the retention period, the items are purged from the mailbox database (no longer recoverable via Outlook/OWA).

To achieve “permanently delete anything older than 90 days” without manual work, an Exchange administrator must:

1. Configure the Deleted Items folder (or the mailbox) with a retention policy or deleted item retention that matches the 90‑day requirement.
2. Optionally adjust the mailbox database or per‑mailbox Deleted item retention period so that items in the Recoverable Items folder are purged after the desired time.

Client‑side Outlook rules cannot:

• Directly empty the Recoverable Items folder.
• Override the server’s deleted item retention logic.

Therefore, the solution is to have the Exchange admin:

• Set a retention policy or folder policy on Deleted Items to delete items older than 90 days.
• Ensure the deleted item retention period on the mailbox/database is set so that items in Recoverable Items are purged on the desired schedule (for example, 90 days, or 90 days plus whatever additional hold is required).

If the Recoverable Items folder is “getting full,” the admin should also review:

• The deleted item retention value for the mailbox/database.
• Any In‑Place Hold or Litigation Hold that might be preventing purging.
• Recoverable Items quotas, which can be configured separately.

End users cannot fully solve this with Outlook rules alone; it must be configured on the Exchange side.

References:

• Recoverable Items folder