SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send out e-mail messages from your email addresses. Without it, you won't be able to use e-mail apps or webmail. Every time 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 managed. Following that, it connects to the remote email server and trades information. When the recipient mailbox is available, your server transmits the email to the receiving POP/IMAP server and the latter delivers that message to the particular mailbox where the receiver can see it. If you want to send emails, you should always make sure that the web hosting company offers the service with their packages. Even if you make use of online form that website visitors use to contact you, you will still require an active SMTP server for your hosting account for the form to function.