SMTP, which is short for Simple Mail Transfer Protocol, is the software that enables you to send out messages from your email addresses. Without this, you won't be able to employ email apps or webmail. Once you send a message, your SMTP server connects to a DNS server to determine where the emails for the recipient domain are handled. Then, it creates a connection to the remote mail server and trades information. When the recipient mailbox is accessible, your server transmits the message to the receiving POP/IMAP server and the latter brings that e-mail to the precise mailbox where the receiver can see it. If you would like to send e-mails, it is recommended to make sure that the hosting company has the service with their plans. Even when you use an online form that visitors use to contact you, you will still need an active SMTP server for your hosting account for the web form to work.