Hi guys!
We've been working on Vetter, our email deliverability testing tool for a couple of months now.
We've done a fair amount of research on the many different reasons your emails might end in spam. These range from technical configuration issues to subtle content changes.
Based on the above, we've compiled a list of email deliverability best practices (44 of them) - as well as explanations as to why each is important. Hopefully, this will be useful for other members of the community.
Check it out here: https://www.monsoonyeti.com/guides/email-deliverability-checklist