Obviously, make sure you have dkim, as well as strict spf and dmarc.
I would suggest sending a simple HTML part along with your plaintext part.
Make sure you're handling bounces and if you can do feedback loop programs[1], do those as well.
Consider making your message a bit longer and specific to your business, so if there's any Bayesian stuff, you might get good vibes. Include your business name and url, etc.
Make sure your mail looks like a real email and not a machine generated low effort mail; have a reasonable subject, put the user's name (as you know it) in to To: with quotes, do something nice for From and Reply-To... etc.
I would suggest sending a simple HTML part along with your plaintext part.
Make sure you're handling bounces and if you can do feedback loop programs[1], do those as well.
Consider making your message a bit longer and specific to your business, so if there's any Bayesian stuff, you might get good vibes. Include your business name and url, etc.
Make sure your mail looks like a real email and not a machine generated low effort mail; have a reasonable subject, put the user's name (as you know it) in to To: with quotes, do something nice for From and Reply-To... etc.
[1] https://support.google.com/mail/answer/6254652?hl=en Google program as example, other large services may have similar