This is a very common issue, and it has to do with either your personal firewall, or your ISP, meaning your Internet Service Provider does not allow you to use an outbound, SMTP server. Since you have configured your mail servers for POP and SMTP as mail.YOURDOMAIN.Com your ISP does not allow you to use your own SMTP server, in this case you will need to contact your ISP, and ask for their "SMTP Server", which will be something like smtp.mail.rcn.net or other.