How do we move entire content of a mailbox folder into another mailbox folder?

[Stuart Torres-Catmur]

We have recently made a change to routing rules so that emails linked to request updates are stored in a dedicated folder instead of being stored in the Deleted Items folder.  The idea is so that going forward, we can periodically empty the Deleted Items folder to keep storage down.

Except...

At the moment we still have all historic emails linked to requests stored in Deleted Items in amongst the genuine trash.

To make this simple, we'd like to move all current Deleted Items into the dedicated folder for requests so that whatever subsequently gets put in Deleted items can be cleared down.

Is there a procedure than can be run to move the entire content of each mailbox's Deleted Items into the dedicated folders we have set up for each mailbox?

Selecting 500 emails at a time isn't practical as in one case there are 150,000 items.