SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send e-mails from your email addresses. Without it, you will not be able to employ e-mail apps or webmail. Once you send an email, your SMTP server connects to a DNS server to discover where the emails for the recipient domain name are taken care of. Following that, it creates a connection to the remote mail server and exchanges information. If the recipient mailbox exists, your server transmits the e-mail to the receiving POP/IMAP server and the latter delivers that email to the particular mailbox in which the recipient can access it. If you'd like to send e-mails, you should always ensure that the website hosting company provides the service with their packages. Even if you use an online form that site visitors use to contact you, you'll still require an active SMTP server for your hosting account for the form to function.