SMTP, which stands for Simple Mail Transfer Protocol, is the software that permits you to send out emails from your email addresses. Without it, you won't be able to use e-mail applications or webmail. When you send a message, your SMTP server creates a connection to a DNS server to discover where the e-mails for the recipient domain name are handled. Subsequently, it creates a connection to the remote email server and trades details. When the recipient mail box is available, your server sends the email to the receiving POP/IMAP server and the latter brings that message to the specific mailbox in which the recipient can see it. If you would like to be able to send emails, you should always make sure that the web hosting company offers the service with their plans. Even when you work with an online form that visitors use to make contact with you, you'll still need an active SMTP server for your hosting account for the web form to operate.