SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows you to send out e-mail messages from your email addresses. Without it, you won't be able to use email applications or webmail. Every time you send an e-mail, your SMTP server creates a connection to a DNS server to discover exactly where e-mails for the recipient domain name are handled. Then, it connects to the remote mail server and exchanges information. In case the recipient mail box is accessible, your server sends the message to the receiving POP/IMAP server and the latter delivers that email to the particular mailbox in which the recipient can access it. If you wish to send emails, it is recommended to make certain that the hosting company has the service with their plans. Even if you work with an 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 web form to work.