SQLite does have an in-memory option but you don’t want to use that here, otherwise it won’t actually be persistent. It’d get destroyed when the app restarts. You want SQLite to persist to a file.

I think OP meant stop as in “unsubscribe”. Ability to unsubscribe is required by law in a lot of places, I’d definitely want to have that in place.

This kind of use case falls under “transactional email” and there are lots of providers you can use for that. Mailgun, AWS SES, Postmark, Sendgrid, and a ton of others. They’re purpose-built for sending one-off emails like this.