I receive an error message in my email program when trying to send mail.
SERVER AUTHENTICATION:
To prevent abuse of email services, we require you to authenticate yourself before being able to send mail from your local computer, via your client-side email program.
To correct this error, and allow for trouble-free email sending, tick the box in your email program that says, "My server requires authentication."
ISP BLOCKING PORT 25:
Some ISPs are now blocking their customers from being able to send outgoing email, from servers outside their network. If you get a Port 25 error message, chances are, your ISP is blocking you.
In your mail program, for outgoing/SMTP email, change the default Port 25 to Port 26.
SSL AUTHENTICATION ERROR:
If you are trying to use SSL without actually purchasing your own SSL certificate, either turn off SSL authentication in your email program OR puchase your own SSL certificate.