We are getting this error message on users PCs when they type in an address or even grab an address from the GAL. It pops up just above the TO: Line as a Mail Tip. Some addresses don't error but others do. Both internal and external address will error. The weird part is that the emails still go through to the user.
I have already tried to clear out the Auto-Complete and it still happens. It is a Mail-Tip so I disabled mail tips and it goes away, but the problem is that then if someone legitimately types in a bad address, it won't give an error then.
Looking for suggestions to this issue.