c-client's POP3 client code is behaving correctly.
A POP3 server that does not advertise USER in CAPA is specifically stating that USER is forbidden; it is the exact equivalent of an IMAP server that advertises LOGINDISABLED. A POP3 client MUST NOT send a USER command to a POP3 server that supports CAPA but does not advertise USER.
Refer to RFC 2449.
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
