Life after Feedburner and their email subscription

I've been using Feedburner for years. Their email subscription feature allowed me to let my subscribers receive an email letting then know when a new post was published.

That feature was shut off on July 1st, 2021,and I'm trying to find a substitute for that. My VPS can send emails, but all of them are detected as spam. I've tried to fix that by adding SPF, DKIM (setting up OpenDkim) and DMARC on my domain, but I've probably made some mistake and the problem persists.

I wonder if someone has the same problem and how has it been solved. I'd prefer the DIY route to save money and avoid the Mailchimps of the world (I've got 1K subscribers, and my blog is a hobby, I wouldn't like to spend money on this).

Any ideas? Maybe some link to a tutorial to fix this?