Is want to find duplicate customers using saved search in netsuite . I want to group customer by their email address domain .. In other words group all customers have same email domain e.g abc@abc.com and def@abc.com so both of these emails have same domain .. Can i do this using a saved search ? if yes , how should i specify filter on email !!

You can use a text formula like this to extract the portion of the email address after the @ character:

SUBSTR({email}, INSTR({email}, '@') + 1)

Have you tried duplicate detection? https://system.netsuite.com/app/help/helpcenter.nl?fid=section_N258211.html