Kill the Newsletter! can be self-hosted, which is extremely nice.

Reading their docs, I was baffled to see that there's no mail server configuration section. Digging into the source code, I discovered that this project uses the SMTP Server package from Nodemailer.

With this package, just with Node.js, an SMTP server instance can be created on the fly. Not will all the capabilities of a regular mail server, but it can intercept and send mails with just a few lines of code.