Search not functioning correctly

I have a contact named John Smith. When you look at an email and hover over his name it shows his email address as

When I search for either John or JohnS it finds all of the emails correctly. When I search for companyx or it doesn’t find any of the emails.

Why can’t it find the correct emails when part or all of the @email address is searched?

Sorry for the delayed reply - I have already discussed this issue with our developers and they told me that they will try to fix it.