SMTP, which is short for Simple Mail Transfer Protocol, is the software that allows you to send messages from your email addresses. Without this, you will not be able to employ e-mail apps or webmail. When you send an e-mail, your SMTP server creates a connection to a DNS server to determine where the emails for the recipient domain name are handled. Then, it connects to the remote mail server and trades information. When the recipient mail box is accessible, your server transmits the e-mail to the receiving POP/IMAP server and the latter brings that e-mail to the particular mailbox in which the recipient can access it. If you would like to be able to send emails, it is recommended to make sure that the web hosting company provides the service with their packages. Even when you make use of online form that website visitors use to make contact with you, you'll still need an active SMTP server for your hosting account for the form to work.