Hello, I use Dynamics CRM 2016 Online and I have a issue with changing regardingobjectid of email. But thanks to the topic below, I found the solution.
https://community.dynamics.com/crm/f/117/t/204446
Now, all I have to do is add <LookupType>... for regardingobjectid from Email entity. So I made a solution includes Email entity, but I can't find "regardingobjectid" from customizations.xml. I also tried with ActivityPointer entity but still can't find it. It seems that there are no default attributes are defined in customizations.xml.
Does anyone know where "regardingobjectid" is defined?