Tips to Improve Email Deliverability and Reply Rates

Hey all, looking for some tips! I use Clay to assign leads into different templates (3 variations) and then plug in variables. So there’s 3 versions of emails going out under 1 campaign. The same campaign mentioned above was really consistent generating 6% replies and booking 1/40 emails for the past week and half. But then the reply drop started declining rapidly in the past 72 hours and this morning is less than 1%. I’m thinking I’m in spam lol (got an automated email telling me that I’m in spam too) I use Instantly DFY for setup/warm up. Wanted to ask if anyone has any tricks to manage/fix deliverability?