SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that enables you to send messages from your email addresses. Without this, you won't be able to employ email applications or webmail. Once you send an e-mail, your SMTP server creates a connection to a DNS server to learn exactly where e-mails for the recipient domain name are handled. After that, it connects to the remote mail server and trades information. When the recipient mailbox is accessible, your server transmits the message to the receiving POP/IMAP server and the latter brings that message to the particular mailbox in which the recipient can see it. If you want to be able to send emails, you should always make sure that the web hosting company has the service with their packages. Even if you make use of online form that site visitors use to contact you, you'll still need an active SMTP server for your hosting account for the form to operate.