Can't receive or send email



I get this mesage when I try to access my email:

Account: 'pop3.frontiernet.net', Server: 'pop3.frontiernet.net', Protocol:
POP3, Server Response: '-ERR invalid command', Port: 110, Secure(SSL): No,
Server Error: 0x800CCC90, Error Number: 0x800CCC18

Can't figure out how to get it up and running again
.