SMTP, which stands 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 use e-mail applications or webmail. Once you send an email, your SMTP server connects to a DNS server to determine where the e-mails for the recipient domain are managed. Following that, it connects to the remote mail server and exchanges information. In case the recipient mailbox is present, your server transmits the e-mail to the receiving POP/IMAP server and the latter delivers that email to the particular mailbox where the recipient can access it. If you want to send e-mails, you should always ensure that the web hosting company offers the service with their packages. Even if you work with an online form that site visitors use to contact you, you still require an active SMTP server for your hosting account for the web form to operate.