SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send e-mails from your email addresses. Without this, you will not be able to employ e-mail apps or webmail. Every time you send an email, your SMTP server connects to a DNS server to find out exactly where e-mails for the recipient domain are managed. Subsequently, it connects to the remote email server and exchanges details. In case the recipient mail box is available, your server sends the email to the receiving POP/IMAP server and the latter delivers that email to the specific mailbox where the recipient can get it. If you want to send e-mails, you should always make sure that the web hosting company has the service with their packages. Even if you use an online form that site visitors use to get hold of you, you still require an active SMTP server for your hosting account for the form to function.