Delete all emails from one sender at once on T-online?

Hello, my question is: is there any way I can delete all emails from eBay classifieds in my T-online mailbox at once?

I got a message from T-online saying that my mailbox will soon be full because there are about 18,000 emails in it, 15,000 of which are from eBay classifieds over the last 20 years, and I would like to delete them all.

The problem is that when I search for all emails with classified ads in the T-online email center, the Select All button disappears and I have to delete each email individually.

Is there any solution to this problem as I would rather not delete 15,000 emails individually.