What characters/length are supported in Mail.app IMAP passwords?

I have longer IMAP and SMTP email passwords than that, using all of those special characters (except maybe $) and have no problems using Mac OS X Mail.app

While it's possible that one of those characters caused the issue, I think that's more likely on the IMAP server side.

As far as I am aware there's nothing in OS X Mail.app which should have prevented that password from working. I know it handles passwords that are 50 characters long and contain a variety of special characters just fine.

If you're concerned, try changing the password again, and if you run into problems try adding length to the password and using letters instead of special characters. Length generally beats complexity for password entropy anyway.