SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that enables you to send e-mail messages from your email addresses. Without it, you will not be able to use email applications or webmail. When you send a message, your SMTP server creates a connection to a DNS server to find out where the emails for the recipient domain name are taken care of. Then, it connects to the remote email server and exchanges details. If the recipient mailbox is accessible, your server transmits the email to the receiving POP/IMAP server and the latter delivers that email to the specific mailbox in which the recipient can find it. If you want to be able to send emails, you should always make sure that the website hosting company provides the service with their packages. Even though you make use of online form that site visitors use to make contact with you, you'll still require an active SMTP server for your hosting account for the web form to function.