[traceroute66]

> Instead, send them a politely worded one-time announcement with an invitation to subscribe.

NO. DO NOT DO THAT !

That is terrible advice and it is against the law.

Opt-in has to be done without inducement and of a person's own volition.

Sending a mail to someone saying "pretty please sign up" is not valid opt-in. It is spamming a bunch of people hoping they will opt-in. It does not matter if you got their mail another way (e.g. if they purchased a product, you can't then spam them trying to get them to opt-in for your mailing list).

One of the fundamental reasons the opt-in law exists is to stop people doing the shit you suggest and ensure that lists are correctly built in a clean manner.

[EGreg]

Under GDPR, can someone send an email to people who 1) downloaded our app, 2) voluntarily entered their email, viewing a message that says if they do that, we can send them a newsletter about how to be more efficient with the app, and 3) selected what kind of person they are, e.g. a teacher, marketer, etc.

But it's been 10 years. Can we send them a newsletter now with an unsubscribe link? Does GDPR have an expiration date on that stuff? Yes it was affirmatively opt-in.

[gpvos]

I'm no expert, but I think that in principle you'd legally be okay. But the 10 years makes it more difficult on a personal level; many, likely most people will have forgotten about you and the permission they gave. Hence my earlier advice.