Email warm-up — what do you recommend?

When I launched my first online course, the plan was simple: collect a database, warm up interest, and send out emails with an offer. Everything was going great until it turned out that more than half of the emails were going to spam. Panic, urgent search for a solution... and someone in the entrepreneurs' chat mentioned automatic email warm-up. That's how I came across top email warm-up https://snov.io/email-warm-up — and that was a turning point. The service began to imitate natural email activity, emails began to get into the "inbox", and the course was still sold. Now, before each launch, I always warm up the mailboxes through it — without risks and nerves.