To the best of my knowledge and according to RFC 1725POP(3) is only used for receiving mail - at least I can find no documentation for any instructions to send mail.

There is one instance I know of where Pop can affect sending mail. That is when sending via SMTP (simple mail transfer protocol) and a server requires authentication. One method that is sometimes used to achieve this is POP before SMTP. If the server required this though and that was the reason for failure, no email could be sent.

Jon