LOLOL NO, it keeps saving. Not a hoarder but obviously have to throw much of that out. Must be thousands in there. And hey, sure would be good to know if that's the problem, or not.
I also think when 99 is hit, the site doesn't save any more and you may have reached an instant auto removal thing?
Nah. We all have way more than 99 messages in our Mailbox's Archive. The Archive saves 100 message links on every page. I have 2,248 pages of archived PMs. That is more than 99.
Just sayin...
I suppose it could be there's a cutoff for the unread PMs page, but it seems unlikely. What's more likely is that the 99+ is just intended as a reminder suggesting that the user do something about those messages.