In Google Spreadsheet you can check whether the value entered is a proper email address by creating a data validation rule. This rule does a simple validation and checks for the @ symbol in the entered value. Let us say you have a column in your spreadsheet that needs to accept only email addresses, then you can do the following to add the validation.
Select the Column values, click the Data menu and select Validation from the menu list.
In the Data Validation window, select Text, Contains for the Criteria drop down and specify the value as @
And if you want to display a message to the user then type the message in Help text some thing like “Enter proper email address example firstname.lastname@example.org”. Click on the Save button to save the changes.
Now when you enter a value in the email address column without the @ symbol then it would display the message as shown below.