SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send emails from your email addresses. Without it, you will not be able to use email apps or webmail. Every time you send an email, your SMTP server connects to a DNS server to learn where the emails for the recipient domain name are handled. Subsequently, it creates a connection to the remote email server and exchanges information. In case the recipient mail box exists, your server sends the message to the receiving POP/IMAP server and the latter delivers that message to the specific mailbox where the recipient can access it. If you wish to send e-mails, you should always make certain that the hosting company provides the service with their plans. Even if you work with an online form that website visitors use to contact you, you will still need an active SMTP server for your hosting account for the web form to function.