SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send out e-mail messages from your email addresses. Without this, you will not be able to employ email apps or webmail. After you send a message, your SMTP server creates a connection to a DNS server to determine exactly where e-mails for the recipient domain are handled. Then, it connects to the remote mail server and exchanges information. In case the recipient mailbox is present, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that message to the particular mailbox in which the recipient can get it. If you want to be able to send e-mails, you should always ensure that the web hosting company has the service with their plans. Even when you use an online form that visitors use to contact you, you'll still need an active SMTP server for your hosting account for the form to function.