SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send emails from your email addresses. Without it, you will not be able to use e-mail apps or webmail. Whenever you send an email, your SMTP server creates a connection to a DNS server to discover where the e-mails for the recipient domain name are handled. Subsequently, it creates a connection to the remote email server and exchanges details. In case the recipient mailbox is accessible, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that message to the precise mailbox in which the receiver can see it. If you want to send e-mails, you should always ensure that the web hosting company has the service with their plans. Even if you use an online form that website visitors use to contact you, you will still require an active SMTP server for your hosting account for the form to operate.