SMTP, which stands for Simple Mail Transfer Protocol, is the software that allows you to send out emails from your email addresses. Without it, you won't be able to use e-mail apps or webmail. Once you send a message, your SMTP server connects to a DNS server to determine where the emails for the recipient domain name are handled. Following that, it creates a connection to the remote email server and exchanges details. If the recipient mail box exists, your server transmits the e-mail to the receiving POP/IMAP server and the latter brings that email to the particular mailbox where the recipient can see it. If you would like to send e-mails, you should always make certain that the web hosting company has the service with their plans. Even though you make use of online form that visitors use to get hold of you, you will still need an active SMTP server for your hosting account for the web form to function.