SMTP, which is short for Simple Mail Transfer Protocol, is the software that allows you to send out messages from your email addresses. Without this, you will not be able to use e-mail applications or webmail. Every time you send an e-mail, your SMTP server connects to a DNS server to discover exactly where e-mails for the recipient domain are taken care of. Subsequently, it connects to the remote email server and exchanges details. In case the recipient mailbox is available, your server sends the message to the receiving POP/IMAP server and the latter delivers that e-mail to the particular mailbox where the recipient can access it. If you'd like to be able to send emails, it is best to make sure that the website hosting company provides the service with their packages. Even though you use an online form that visitors use to make contact with you, you still require an active SMTP server for your hosting account for the form to function.