SMTP, which is short 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 email applications or webmail. After you send a message, your SMTP server connects to a DNS server to learn where the e-mails for the recipient domain are managed. Following that, it connects to the remote email server and trades details. In case the recipient mail box is available, your server sends the email to the receiving POP/IMAP server and the latter delivers that e-mail to the specific mailbox where the recipient can find it. If you wish to send e-mails, it is best to make certain that the web hosting company has the service with their packages. Even if you make use of online form that website visitors use to make contact with you, you'll still require an active SMTP server for your hosting account for the form to operate.