RE: Field to show if a Contact has a duplicate
Hi
As suggested by T.I.A, better to stick to CRM Out of the box duplicate detection functionalities. However, if you definitely want a flag field on Contact to see if there is duplicate or not, you could try the following
01. Create Flow that triggers on Contact Create / Update and queries and checks if there are more than one contacts with the same email, you can update the record flag field value.
02. You can write a plugin that triggers on Pre/post update and checks and sets the flag
03. You could create a custom workflow activity to check and set the flag and call the CWA in a workflow that triggers on Create of the record or update of email field.