SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send out messages from your email addresses. Without it, you will not be able to employ email applications or webmail. Whenever you send an email, your SMTP server connects to a DNS server to find out where the emails for the recipient domain are managed. Following that, it connects to the remote mail server and exchanges information. In case the recipient mail box exists, your server sends the email to the receiving POP/IMAP server and the latter delivers that message to the particular mailbox in which the receiver can see it. If you want to send e-mails, it is recommended to make sure that the web hosting company provides the service with their plans. Even if you use an online form that website visitors use to contact you, you'll still need an active SMTP server for your hosting account for the form to function.