SMTP, which stands 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 apps or webmail. Once you send an e-mail, your SMTP server creates a connection to a DNS server to find out where the e-mails for the recipient domain name are handled. Subsequently, it creates a connection to the remote email server and trades details. When the recipient mail box is accessible, your server sends the message to the receiving POP/IMAP server and the latter brings that email to the particular mailbox in which the receiver can find it. If you wish to be able to send e-mails, you should always ensure that the hosting company has the service with their packages. Even if you make use of online form that visitors use to contact you, you still need an active SMTP server for your hosting account for the web form to function.