SMTP, which stands for Simple Mail Transfer Protocol, is the software that enables you to send out emails from your email addresses. Without it, you won't be able to use email 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 name are handled. After that, it creates a connection to the remote mail server and exchanges details. In case the recipient mailbox exists, your server transmits the email to the receiving POP/IMAP server and the latter brings that e-mail to the precise mailbox in which the recipient can find it. If you want to send e-mails, you should always make sure that the website hosting company offers the service with their plans. Even when you make use of online form that website visitors use to make contact with you, you will still require an active SMTP server for your hosting account for the web form to work.