SMTP, which is short for Simple Mail Transfer Protocol, is the software that permits you to send out messages from your email addresses. Without this, you will not be able to use e-mail applications or webmail. When you send a message, your SMTP server creates a connection to a DNS server to discover where the e-mails for the recipient domain name are handled. Following that, it connects to the remote mail server and exchanges details. When the recipient mailbox is available, your server transmits the message to the receiving POP/IMAP server and the latter delivers that e-mail to the particular mailbox where the receiver can see it. If you would like to be able to send e-mails, it is best to ensure that the hosting company has the service with their packages. Even if you make use of online form that site visitors use to contact you, you'll still require an active SMTP server for your hosting account for the form to operate.