SQL Query taking too much time to fetch single data

Question

Dear all,

My SQL DB size is 150 GB.

I am fetching record from a simple query but its execution takes too much time (Approx. 1 Min)

My Query is:

SELECT * FROM DELIVERY WHERE EMAILId='[email protected]'

(Note: EmailID is not primary key or clustered index or non clustered index).

Please guide me so that i can improve the query performance.