SMTP, which stands for Simple Mail Transfer Protocol, is the software that enables you to send out e-mails from your email addresses. Without it, you won't be able to employ email apps or webmail. Once you send an email, your SMTP server creates a connection to a DNS server to determine where the emails for the recipient domain are handled. Subsequently, it creates a connection to the remote mail server and exchanges information. When the recipient mail box is available, your server transmits the email to the receiving POP/IMAP server and the latter brings that email to the particular mailbox in which the receiver can access it. If you would like to send e-mails, it is best to ensure that the web hosting company has the service with their packages. Even when you use an online form that visitors use to make contact with you, you still need an active SMTP server for your hosting account for the form to function.