I didn't want to pay for expensive vocabulary apps that often start with beginner words while I am looking for advanced vocabulary, so I built it myself.
I built a comparable system that sends me an email every day that I can respond to, to maintain a journal; it works like described above and has been running for about 5 years now with zero downtime.
Anyway the idea is really good!
Don't need that. You're already paying for (or self host) your primary email address right? That includes sending emails from that email address. Use those same login credentials to send emails to yourself, no need to contract a third party for sending a handful of emails per day, especially to yourself
Although, I appreciate the idea and wish luck with learning the language (as NT2 I assume). Questions welcome.
Are you reinventing a stove-pipe version of Anki, based on cloud services and e-mail?
Are you really going to send yourself 300 e-mails when 300 cards are due that day?