How to avoid spam block when emailing 1k consenting users on new site?

I've set up a live product which has collected a few thousand emails through account registrations. They have consented for marketing emails, but never been sent them.

The emails are on Supabase and could be easily exproted - but what sort of things should I look out for reguarding getting spam blocked?

We've done a major major feature change that active users love, but a lot of older 2022 users don't know about it! Hence we want to kick up a newsletter, once every few months. Is there things to look out for regarding SMTP, or avoiding spam blockers these days? I remember sending emails back in the day with PHP just fine, but understand a bulk email to 1k emails with half of them on gmail would probably be spam-blocked en-masse these days. Is that true, and if so, is it at all avoidable, given it's not a sale/promo newsletter, but quite a big feature change?