SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send e-mail messages from your email addresses. Without this, you won't be able to employ e-mail applications or webmail. Once you send an email, your SMTP server connects to a DNS server to determine exactly where e-mails for the recipient domain are handled. After that, it creates a connection to the remote mail server and trades details. In case the recipient mailbox exists, your server sends the email to the receiving POP/IMAP server and the latter brings that e-mail to the specific mailbox in which the receiver can see it. If you want to send e-mails, it is best to make sure that the website hosting company has the service with their plans. Even when you work with an online form that site visitors use to get hold of you, you'll still need an active SMTP server for your hosting account for the form to work.