SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send out e-mails from your email addresses. Without it, you will not be able to use email applications or webmail. Whenever you send a message, your SMTP server connects to a DNS server to discover where the e-mails for the recipient domain are taken care of. Subsequently, it creates a connection to the remote email server and exchanges information. If the recipient mailbox is available, your server sends the message to the receiving POP/IMAP server and the latter brings that email to the precise mailbox where the recipient can access it. If you'd like to send emails, you should always make sure that the website hosting company offers the service with their packages. Even if you work with an online form that visitors use to get hold of you, you still require an active SMTP server for your hosting account for the web form to function.