SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that enables you to send out emails from your email addresses. Without it, you will not be able to employ e-mail applications or webmail. Every time you send an e-mail, your SMTP server connects to a DNS server to discover exactly where e-mails for the recipient domain are managed. Then, it connects to the remote mail server and exchanges information. If the recipient mailbox exists, your server sends the email to the receiving POP/IMAP server and the latter delivers that email to the particular mailbox where the receiver can get it. If you would like to be able to send e-mails, you should always make certain that the hosting company offers the service with their plans. Even if you make use of online form that website visitors use to get hold of you, you will still need an active SMTP server for your hosting account for the form to work.