Many mail servers, including fastwebhost's, are set up with pop-before-smtp. This is a Perl script that allows email relay control based on successful POP / IMAP logins.

In other words, you need to establish a valid POP or IMAP connection to your e-mail account before you can send e-mails.

 If your e-mail client hasn't fetched your e-mail for more than 30 minutes and you try to send a message, you will most probably receive the following error:

"Perhaps you have not logged into the pop/imap server in the last 30 minutes or do not have SMTP Authentication turned on in your email client."

The solution is simple, you have to restart your e-mail client and fetch the new messages. Once you have done that, you will be able to send new emails.