SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows you to send out emails from your email addresses. Without it, you won't be able to use email apps or webmail. After you send a message, your SMTP server creates a connection to a DNS server to determine exactly where emails for the recipient domain are handled. Subsequently, it creates a connection to the remote email server and exchanges information. In case the recipient mailbox is available, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that e-mail to the precise mailbox in which the receiver can access it. If you would like to be able to send emails, you should always make certain that the web hosting company provides the service with their plans. Even if you make use of online form that site visitors use to make contact with you, you still need an active SMTP server for your hosting account for the form to work.