I find the word find & replace difficult to use. Would you consider using Excel rather?

Paste/ import all email addresses into an excel spreadsheet.

Select the entire column which contains the email addresses.

Go to the 'data' tab in the ribbon and press on 'text to columns'

Leave on 'delimited' option and press next.

Under 'delimiters' choose other and type @ into the box.

press next, leave on 'general' format, and press finished.

Now you should have all the domains separate from the user names.

HTH

Sixhobbts