I'm pretty sure it is at it's maximum, but I'm not %100 sure about that one. I'll look into it ASAP.
*EDIT*
I have looked into it, but unfortunately the inbox has a limit of 50 messages and cannot exceed that. I can lower it, but that would be the complete opposite of what you asked. However, the savebox also has a limit of 50 messages. Perhaps you could put some of the posts into there for a total of 100 messages. And again, sorry.