SMTP, which is short for Simple Mail Transfer Protocol, is the software that allows you to send out e-mail messages from your email addresses. Without this, you won't be able to employ e-mail apps or webmail. Every time you send an email, your SMTP server connects to a DNS server to find out where the e-mails for the recipient domain name are handled. Subsequently, it connects to the remote mail server and exchanges details. In case the recipient mailbox is present, your server sends the e-mail to the receiving POP/IMAP server and the latter brings that message to the precise mailbox where the recipient can get it. If you'd like to be able to send emails, it is best to make sure that the website hosting company provides the service with their plans. Even if you work with an online form that website visitors use to get hold of you, you'll still need an active SMTP server for your hosting account for the web form to operate.