To validate an email address in Excel, you can use filters and data validation. Filters are an easy way to add rules against which every entry in a column will be checked. When the filter is applied, only rows that match the filter rules will be shown.
Using data validation is a little more complicated, but is a slightly more robust method of validating email addresses. You can add a custom function to search strings inside the cells and highlight strings that do not match the formula rules.