SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send messages from your email addresses. Without it, you won't be able to use e-mail apps or webmail. When you send a message, your SMTP server connects to a DNS server to learn where the emails for the recipient domain are managed. Then, it creates a connection to the remote email server and trades details. When the recipient mailbox is present, your server transmits the email to the receiving POP/IMAP server and the latter brings that message to the specific mailbox in which the receiver can get it. If you would like to be able to send e-mails, it is recommended to make certain that the web hosting company offers the service with their plans. Even if you use an online form that website 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.