Welcome to MyBB!

So, I did a little testing. Posts are restricted to 65535 characters. PMs are not: when I previewed a post with the entirety of The Pointless Adventures of Nopor Puss, it told me that it was something over 150k characters. However, I was able to PM the exact same text to myself with no issues. Not sure if this actually needs to have anything done about it, just noting it for the record.

Also, PMs are set to some restrictions that I presume are defaults for this software; you can only send to five people at a time, and I think you can only have something like 100 total. I think it's a good idea to raise those limits.