Regex empty string or email

Question

I found a lot of Regex email validation in SO but I did not find any that will accept an empty string. Is this possible through Regex only? Accepting either empty string or

Answer 1

this will solve, it will accept empty string or exact an email id

"^$|^([\w\.\-]+)@([\w\-]+)((\.(\w){2,3})+)$"