SMTP, which is an acronym for Simple Mail Transfer Protocol, is the software that allows you to send out e-mail messages from your email addresses. Without it, you won't be able to use email apps or webmail. Whenever you send an email, your SMTP server creates a connection to a DNS server to find out where the e-mails for the recipient domain name are managed. Following that, it creates a connection to the remote email server and trades details. In case the recipient mailbox is present, your server sends the e-mail to the receiving POP/IMAP server and the latter delivers that e-mail to the specific mailbox in which the recipient can find it. If you want to send emails, you should always ensure that the website hosting company provides the service with their plans. Even though you work with 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 form to operate.