SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that enables you to send e-mail messages from your email addresses. Without it, you won't be able to use e-mail applications or webmail. When you send an email, your SMTP server connects to a DNS server to discover exactly where e-mails for the recipient domain are taken care of. After that, it connects to the remote email server and trades details. If the recipient mail box exists, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that e-mail to the precise mailbox where the receiver can get it. If you'd like to be able to send emails, it is best to make sure that the web hosting company provides the service with their packages. Even if you use an online form that visitors use to get hold of you, you'll still need an active SMTP server for your hosting account for the form to work.