SMTP, which is short for Simple Mail Transfer Protocol, is the software that allows you to send e-mails from your email addresses. Without it, you will not be able to use e-mail applications or webmail. After you send a message, your SMTP server connects to a DNS server to discover where the emails for the recipient domain name are managed. After that, it creates a connection to the remote email server and trades details. If the recipient mailbox exists, your server transmits the email to the receiving POP/IMAP server and the latter delivers that e-mail to the particular mailbox where the recipient can find it. If you'd like to send emails, it is recommended to make sure that the website hosting company has the service with their plans. Even if you make use of online form that visitors use to contact you, you will still need an active SMTP server for your hosting account for the form to function.