SMTP, which stands for Simple Mail Transfer Protocol, is the software that permits you to send emails from your email addresses. Without this, you won't be able to use e-mail applications or webmail. Once you send a message, your SMTP server creates a connection to a DNS server to find out exactly where e-mails for the recipient domain name are handled. Then, it connects to the remote email server and exchanges information. In case the recipient mailbox is accessible, your server transmits the email to the receiving POP/IMAP server and the latter brings that e-mail to the specific mailbox in which the recipient can get it. If you wish to send emails, you should always make sure that the website hosting company provides the service with their plans. Even if you use an online form that visitors use to get hold of you, you'll still require an active SMTP server for your hosting account for the web form to operate.