SMTP, which stands for Simple Mail Transfer Protocol, is the software that allows you to send out messages from your email addresses. Without this, you won't be able to employ email applications or webmail. When you send an email, your SMTP server creates a connection to a DNS server to determine where the emails for the recipient domain are managed. Then, it connects to the remote email server and exchanges details. In case the recipient mail box exists, your server transmits the email to the receiving POP/IMAP server and the latter delivers that email to the precise mailbox in which the recipient can access it. If you'd like to send emails, you should always make certain that the website hosting company has the service with their plans. Even if you use an online form that site visitors use to contact you, you will still need an active SMTP server for your hosting account for the web form to operate.