SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send out e-mail messages from your email addresses. Without this, you will not be able to use e-mail apps or webmail. When you send an e-mail, your SMTP server creates a connection to a DNS server to determine exactly where emails for the recipient domain are managed. Subsequently, it creates a connection to the remote email server and exchanges information. If the recipient mailbox exists, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that message to the precise mailbox in which the recipient can see it. If you'd like to be able to send e-mails, you should always make certain that the website hosting company has the service with their plans. Even if you use an online form that site visitors use to contact you, you will still require an active SMTP server for your hosting account for the form to work.