Tell us you don't understand how the "From" header works without telling us.

FYI, that is really just a text string. Most providers don't let you change it, but its not exactly hard to falsify. People are largely ignorant of the fact that email mostly isnt trustworthy. Spammers abuse this ignorance constantly.

In order to send email as another address, gmail requires you to verify the address by sending you an email there first. AFAIK, they never re-verify, but that's the main weakness I see.