Question : get wrong autodiscover server in warning message....

We had another CAS server at one point that was used for autodiscover and we have since replaced it. However, there are some clients externally, using RPC over HTTPS that are getting a warning:

Allow this website to configure user@domain.com server settings?
https://oldserver.domain.com
Your account was redirected....

I've checked through external DNS, internal DNS, the current IIS autodiscover directory, and the domain controllers and I can't find any reference to this old server so I don't know where these outlook clients are getting this from. How can I update them to use the new one and get rid of the warning messages for a server that doesn't even exist anymore?

Answer : get wrong autodiscover server in warning message....

I found the source I think. I was looking for A records and CNAME records but on the different tab of our external DNS there was a SRV records entry pointing to the old one.