SMTP, which stands for Simple Mail Transfer Protocol, is the software that enables you to send out emails from your email addresses. Without it, you won't be able to use e-mail applications or webmail. After you send an email, your SMTP server creates a connection to a DNS server to find out where the emails for the recipient domain are handled. After that, it connects to the remote mail server and exchanges details. In case the recipient mail box is accessible, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that message to the particular mailbox in which the recipient can access it. If you would like to send emails, you should always make certain that the website hosting company provides the service with their plans. Even though you use an online form that site visitors use to contact you, you'll still need an active SMTP server for your hosting account for the form to operate.