SMTP, which stands for Simple Mail Transfer Protocol, is the software that permits you to send messages from your email addresses. Without it, you won't be able to use email applications or webmail. Every time you send a message, your SMTP server creates a connection to a DNS server to find out where the e-mails for the recipient domain are managed. After that, it connects to the remote mail server and exchanges information. If the recipient mail box exists, your server sends the e-mail to the receiving POP/IMAP server and the latter delivers that message to the specific mailbox where the recipient can get it. If you want to be able to send emails, it is best to make certain that the web hosting company offers the service with their packages. Even if you use an online form that site visitors use to make contact with you, you still require an active SMTP server for your hosting account for the form to work.