How to: SMTP Header Injection
https://www.acunetix.com/blog/articles/email-header-injection/
# It is common practice for web pages and web applications to implement contact forms, which in turn send email messages to the intended recipients. Most of the time, such contact forms set headers. These headers are interpreted by the email library on the web server and turned into resulting SMTP commands, which are then processed by the SMTP server.
```POST /contact.php HTTP/1.1```
```Host: www.example2.com```
``` ```
```name=Best Product\nbcc: everyone@example3.com&replyTo=blame_anna@example.com&message=Buy my product!```