SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that enables you to send emails from your email addresses. Without it, you will not be able to employ e-mail apps or webmail. Once you send an email, your SMTP server creates a connection to a DNS server to learn exactly where emails for the recipient domain name are taken care of. After that, it connects to the remote email server and exchanges information. In case the recipient mailbox is accessible, your server sends the message to the receiving POP/IMAP server and the latter brings that email to the specific mailbox in which the receiver can see it. If you wish to be able to send e-mails, it is recommended to make sure that the web hosting company has the service with their packages. Even when you use an online form that site visitors use to contact you, you'll still require an active SMTP server for your hosting account for the web form to work.