Hi Mrigesh, I would recommend to stick to declared ID (customer ID) for
all use cases, and use the appropriate profile merge rule preferably
with Last Auth as auth option.Even, when someone is opening the email
and clicking on the link to go to landing page, you can implement ID
sync on that page. You need to use appropriate macros in Adobe Campaign,
so the customer ID/hashed ID is passed as URL parameter. Then perform an
ID sync with that customer ID/hashed ID. Thanks,Varun Kalra