SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send out messages from your email addresses. Without it, you won't be able to use e-mail applications or webmail. After you send a message, your SMTP server connects to a DNS server to learn exactly where emails for the recipient domain are taken care of. After that, it connects to the remote mail server and exchanges information. If the recipient mailbox is present, your server transmits the email to the receiving POP/IMAP server and the latter delivers that e-mail to the particular mailbox in which the recipient can access it. If you'd like to be able to send emails, it is best to ensure that the hosting company has the service with their plans. Even if you make use of online form that website visitors use to make contact with you, you will still require an active SMTP server for your hosting account for the form to operate.