Trying to log in to POP3 server without permission


New Email
I have two accounts with Fastmail, one paid and one guest. I just received a notice saying that I had attempted to log in to a POP server on my guest account, and that wasn't permitted. Since I always log in in the same fashion (user name and password, then click; there are no other options), I have no idea what they're referring to. Since there's no support on the guest account, I can't find out. Has anyone had a similar experience, or have knowledge of how this could happen? Should I care?