@mslnrd  This is likely caused by LDAP on 636 uses referrals that can your initial query can be referred to across the entire domain tree across multiple LDAP servers. So somewhere within that referral your issues arrises in the hostname verification. Switching to the global catalog port 3269 and there are no referrals.  I can't speak to the issues within your ldaps servers causing the issue within the referrals, but makes sense why switching to the secure global catalog port resolved your issue.   Hope this clarifies why the change in port resolved your issue. If you found that the provided solution(s) assisted you with your query, please take a moment to login and click Accept as Solution below each response that helped. Thank you, Matt ... View more