The name and sending address are equally easy to "spoof". You can rely on neither in identifying the sender of mail. This is one of the reasons Thunderbird scam detector ignores the senders email address, Likewise the spam filter can be instructed to whitelist the senders email addresses in your address book, but it by design pays no attention to the sender in determining if a mail is spam. Finally, Thunderbird will use the display name from your address book in favor of the display name in the sender address. SO if a mail comes in from Lucy <lucyjones@gmail.com>, thunderbird will display "Aunt Lucy" if that is the name associated with the email address in your address book. So you get a defacto check on your contacts by having your choice of display name appear.