Are you seeing these sent messages landing in the Junk Email/Spam folders in Gmail, or are they not getting there at all? If they're not getting there at all, do a search in your Delivery log for the gmail address you sent to and make sure to Display Related Traffic. That should return the SMTP session between your server and Google and you should then see why it failed. I hope that helps!

Based on a previous participant's post, Google will probably block you for 30 days after your infection is resolved.  The logs should confirm.   SM version probably does not matter.