Yes, the problem is that many MX servers do not have their spam defences setup in the right order, especially in the case where you reply to someone who has alr

Yes, the problem is that many MX servers do not have their spam defences setup in the right order, especially in the case where you reply to someone who has already emailed you: The recipient's server should always check if your email is authenticated (SPF, DKIM). If so, they should check if their user has emailed you in the past, and if so they should let your email through, to prevent it being marked as a false positive. They should try and do this even if your domain happens to land on a single DNS blacklist (or they should use a quorum of DNS blacklists).