What's the storage limit for inbox messages?

So, I’ve been getting quite a few DMs lately. As soon as I hit the 50 mark, I start clearing out the older, less important ones just to make room. Honestly, it's becoming a bit of a chore... I was wondering if anyone knows the exact limit before the inbox actually hits capacity?

Folder Controls
Messages in Inbox: ...
Total posts: ..., out of a limit of ...

More accurately, 75. I just noticed that now. 😵