sending e-mails from your app.

If you want to send e-mails from your application, check out https://www.mailgun.com/. You can register for free and with your free account you can also send a good number of e-mails. And if you pay for it, you can send thousands of mails if you want. Their service can be used from Bash, Python, PHP, etc.

On my VPS I used a command-line solution (see here) that sends e-mails with sendmail. Unfortunately, Gmail treats these mails as spam, so it’s not appropriate for sending messages to other people. Mailgun is a better solution.