# SMTP Server

*Internet standard*. An app or server that sends email and react to response codes from receiving servers.

An SMTP server sends email using [SMTP][smtp]. An SMTP server doesn't describe the physical (or virtual) server, but the [application][] on it that runs in the background waiting to send mail.

[application]: https://www.twilio.com/en-us/blog/insights/what-is-an-smtp-server

[smtp]: /docs/sendgrid/glossary/smtp