SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send e-mails from your email addresses. Without it, you won't be able to use email apps or webmail. Every time you send an email, your SMTP server creates a connection to a DNS server to discover where the e-mails for the recipient domain are taken care of. After that, it connects to the remote email server and exchanges details. In case the recipient mailbox is accessible, your server sends the email to the receiving POP/IMAP server and the latter delivers that email to the particular mailbox in which the receiver can see it. If you would like to be able to send emails, you should always ensure that the website hosting company has the service with their plans. Even though you use an online form that site visitors use to contact you, you'll still require an active SMTP server for your hosting account for the form to function.
