A protocol is a language that the computer uses. Most email is sent using smtp (simple mail transport protocol). And most home email is collected using pop (post office protocol). Most sending email problems I have seen stem from the fact that the ISP (internet service provider like BT or wannadoo) will not send emails to smtp servers that are not theirs. As an example, my ISP (NTLworld) will not send emails to the mail.freeserve.net mail servers (freeserve's smtp server) you can only send them to smtp.ntlworld.com. A more recent thing I have seen is that the BTInternet smtp server requires authentication (you have to provide a username and password in order to send mail). This is an anti-spam thing apparently. Does this sound familiar?