SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send out e-mails from your email addresses. Without this, you will not be able to use email apps or webmail. Every time you send a message, your SMTP server connects to a DNS server to discover where the e-mails for the recipient domain name are handled. Following that, it connects to the remote email server and exchanges information. When the recipient mailbox is available, your server sends the message to the receiving POP/IMAP server and the latter delivers that message to the particular mailbox where the recipient can access it. If you'd like to be able to send emails, it is best to ensure that the website hosting company offers the service with their packages. Even when you make use of online form that visitors use to make contact with you, you'll still need an active SMTP server for your hosting account for the web form to work.