(Sorry - not sure if this is the best category.)
Somewhat to my surprise, you can PM a suspended member. Nothing pops up to say “sorry - member is suspended for the next 200 years, so don’t hold your breathe waiting for a reply” or anything like that. (It does take you to their profile page, where the suspended message is displayed, but how many users intent on sending a PM will stop to read that?) If an ordinary member PMs a suspended member, no notification e-mail is sent, but if a moderator sends a PM, the e-mail is sent (which will annoy them if they try to log in to reply…).
Equally oddly, you can invite a suspended member to participate in an e-mail discussion - again, with no warnings or error messages. As far as I can tell, no e-mail is sent in these circumstances, whether the invitation comes from an ordinary member or a moderator.
A more consistent approach would seem to be called for here. My suggestion would be to completely disable PMs and invites for suspended members.