SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows 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 an e-mail, your SMTP server creates a connection to a DNS server to determine exactly where e-mails for the recipient domain name are handled. Then, it connects to the remote email server and exchanges details. When the recipient mail box is present, your server transmits the message to the receiving POP/IMAP server and the latter brings that message to the particular mailbox in which the recipient can get it. If you want to send e-mails, it is recommended to make sure that the website hosting company provides the service with their packages. Even if you use an online form that site visitors use to make contact with you, you will still require an active SMTP server for your hosting account for the web form to work.