SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that permits you to send out e-mails from your email addresses. Without it, you won't be able to use e-mail applications or webmail. After you send an email, your SMTP server creates a connection to a DNS server to determine exactly where emails for the recipient domain are handled. Then, it creates a connection to the remote email server and trades details. When the recipient mailbox exists, your server sends the message to the receiving POP/IMAP server and the latter brings that email to the precise mailbox where the receiver can access it. If you want to send e-mails, it is recommended to ensure that the website hosting company offers the service with their plans. Even though you make use of online form that visitors use to contact you, you'll still need an active SMTP server for your hosting account for the form to operate.