SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows you to send out emails from your email addresses. Without this, you won't be able to use email applications or webmail. Every time you send an e-mail, your SMTP server creates a connection to a DNS server to discover where the emails for the recipient domain name are handled. Subsequently, it creates a connection to the remote email server and trades information. In case the recipient mailbox is available, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that email to the specific mailbox where the receiver can see it. If you would like to be able to send e-mails, it is best to make sure that the hosting company has the service with their packages. Even though you make use of online form that visitors use to make contact with you, you'll still require an active SMTP server for your hosting account for the web form to function.