SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows you to send out emails from your email addresses. Without this, you will not be able to use e-mail applications or webmail. When 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 mail server and exchanges information. If the recipient mailbox is accessible, your server sends the message to the receiving POP/IMAP server and the latter brings that e-mail to the specific mailbox in which the recipient can find it. If you want to be able to send emails, it is recommended to make certain that the hosting company offers the service with their plans. Even though you use an online form that site visitors use to get hold of you, you'll still need an active SMTP server for your hosting account for the web form to operate.