SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send messages from your email addresses. Without it, you won't be able to employ e-mail applications or webmail. Whenever you send an e-mail, your SMTP server creates a connection to a DNS server to learn exactly where emails for the recipient domain name are handled. Then, it creates a connection to the remote email server and trades details. In case the recipient mail box is present, your server transmits the email to the receiving POP/IMAP server and the latter brings that email to the specific mailbox where the receiver can find it. If you wish to send e-mails, you should always make sure that the website hosting company has the service with their plans. Even when you make use of online form that website visitors use to contact you, you still require an active SMTP server for your hosting account for the form to operate.