If you can not send mail, there are two possible reasons.

1. The most common reason is that port 25 is being blocked by your ISP. 
   If you are not using a laptop, or otherwise always use your computer from the same location, you can use your ISP's smtp server instead of our's.  Most ISP's will let you send using their server regardless of what you enter for the from address.  Your customer's will never know the difference. 
   
   Using your ISP's mail server is the preferred method of sending mail since it will be faster than sending to any other server on the Internet.  However, if you can not use your ISP's mail server, or you are using a laptop and can't always use your ISP's mail server, you can change the SMTP port in your mail client to port 587 instead of port 25.
   
2. The other common reason for not being able to send mail is that you are not sending your password when you send the mail.
   Our mail servers require you to send the password to send mail as well as recieving it.  Make sure you've set your mail client up to send the password for both send and recieve.

Done