SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send out e-mail messages from your email addresses. Without it, you will not be able to use email apps or webmail. Every time you send an email, your SMTP server connects to a DNS server to learn exactly where emails for the recipient domain name are taken care of. After that, it creates a connection to the remote email server and trades details. In case the recipient mail box exists, your server sends the email to the receiving POP/IMAP server and the latter brings that message to the particular mailbox in which the receiver can find it. If you'd like to send e-mails, it is best to make sure that the web hosting company offers the service with their packages. Even though you use an online form that visitors use to get hold of you, you will still need an active SMTP server for your hosting account for the form to operate.