SMTP, which stands for Simple Mail Transfer Protocol, is the software that permits you to send out e-mails from your email addresses. Without this, you won't be able to use e-mail apps or webmail. Whenever you send a message, your SMTP server connects to a DNS server to find out where the e-mails for the recipient domain are handled. Following that, it creates a connection to the remote mail server and trades information. When the recipient mailbox exists, your server transmits the email to the receiving POP/IMAP server and the latter brings that e-mail to the specific mailbox where the recipient can find it. If you would like to send e-mails, you should always make sure that the hosting company has the service with their packages. Even if you use an online form that visitors use to get hold of you, you will still need an active SMTP server for your hosting account for the web form to work.