SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send e-mails from your email addresses. Without it, you won't be able to use email applications or webmail. Whenever you send a message, your SMTP server creates a connection to a DNS server to learn exactly where emails for the recipient domain are managed. Then, it creates a connection to the remote email server and exchanges details. If the recipient mail box exists, your server sends the email to the receiving POP/IMAP server and the latter brings that e-mail to the particular mailbox where the receiver can access it. If you wish to be able to send emails, you should always make sure that the website hosting company offers the service with their packages. Even if you use an online form that visitors use to make contact with you, you'll still require an active SMTP server for your hosting account for the web form to operate.