how are people obtaining email addresses in 2026?

Same way as always, people giving it to you because they want something: a useful checklist, a discount, a newsletter that's actually worth reading. Put the form where people already are, end of your most popular posts usually beats a popup. Don't buy lists. Apart from the legal side (GDPR if you have any EU contacts), Gmail and Yahoo have got strict about spam complaints, and a bought list will wreck your sending domain fast.