Hello

You can Test your email score at this website:
https://www.mail-tester.com/

After see your email score you can find your problems
And solve problem
Also please check your your ip address in blacklist
you can use mxtoolbox:
https://mxtoolbox.com/blacklists.aspx

Your mails are likely to go to spam or even disappear in a black hole when sending to Google or Hotmail/Outlook because your mail server does not have a good enough reputation according Google/Microsoft.

You can relay mail to Google/Outlook via a party that has a good reputation. Like smtp2go or the SendGrid API (and there are more companies like this)

Hopefully no emails goes in inbox from DO :-( whether you have everything up to the mark as per email standard..