OK, I have no idea where to put this and this happened to be my choice.
Is it impossible for the mods or admins to increase the number of PMs I can receive?
Cut and past the old messages into a Word (or whatever) document, and then delete them.
You could have put it in the Community & Forum Issues forum…
Just delete old ones. I only keep the ones that are somewhat important. Try deleting the old ones you’ve sent, usually really only need the replies.
You can save as many messages as you like, because you can download private messages to a text file on your computer. Then you can delete the oldest messages to make room to receive new ones. Every time you save, you can delete your oldest sent and received messages. I like that.