SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send emails from your email addresses. Without it, you won't be able to employ e-mail applications or webmail. Whenever you send a message, your SMTP server connects to a DNS server to learn where the e-mails for the recipient domain name are taken care of. Subsequently, it connects to the remote mail server and exchanges information. When the recipient mailbox is present, your server transmits the e-mail to the receiving POP/IMAP server and the latter delivers that message to the particular mailbox in which the receiver can see it. If you wish to send emails, you should always make sure that the web hosting company provides the service with their packages. Even when you use an online form that visitors use to get hold of you, you still need an active SMTP server for your hosting account for the form to work.