The server responded: -ERR [SYS/PERM] pop not allowed for user.this is what i get when i 'm using outlook?

Log onto incoming mail server (POP3): Your e-mail server rejected your login. Verify your user name and password for this account in Account Settings. The server responded: -ERR [SYS/PERM] pop not allowed for user. This is a error when i'm trying to connect to my incoming mail server ,outgoing works fine.What can i do