@Gellison You can use flash fill to extract the domain name in an adjacent column, then use that to sort by. To do this, assuming your email addresses are in column A (can be wherever), in column B you'd just type out the entire domain name. Excel will recognize this. Go to the next cell and start typing the domain name. As soon as Excel recognizes the pattern, it will fill in the range with light gray text of all matching records. When it looks good, confirm with ENTER.
The above is opposed to entering a formula manually. In which case I'd use a formula like: