SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows you to send emails from your email addresses. Without it, you will not be able to use email apps or webmail. When you send an e-mail, your SMTP server creates a connection to a DNS server to find out exactly where emails for the recipient domain name are handled. Subsequently, it creates a connection to the remote mail server and exchanges details. If the recipient mailbox is present, your server transmits the email to the receiving POP/IMAP server and the latter delivers that e-mail to the specific mailbox where the receiver can get it. If you wish to be able to send emails, you should always make certain that the hosting company has the service with their plans. Even if you make use of online form that website visitors use to contact you, you still need an active SMTP server for your hosting account for the web form to operate.