In order to flag dips you will need a new table with a key field of the value you are looking for duplicates of. So for example email address.
Initially populate that table with a summary report grouping in email address and copy over to the email table.
Then make a relationship back to the details table based in email address and you can then make s uammrubif the # of details for each email address.
Look up that summary count down to the daetals and you will have your flag Then to auto maintain it, I like to create a field on t(e parent tale called email exists? As a formula checkbox field set to the formula
True
Then look that up down to the details Record.
Then set up an Automation to fire and add a record in the email parent table when a record is added or modified and the email exists lookup field is false.