Maybe not the answer you're looking for, but if it's not a rush you can probably do it manually. 8k is not so much, you can probably go through it with a couple minutes a day for a few weeks, or within a week if you take like 30 minutes a day.

If you're going through an email every 2 seconds it's only a little over 4 hours of work which isn't too bad. And for the most part you'll probably be skimming senders/subjects so it won't take anywhere near 2 seconds per email.