UNIX geekery ahead. Skip to save your sanity.
Over the years I've needed a script to set the From: line in a mail that it sends out - and the syntax is quite obscure and doesn't always turn up in a Goolgle search.
So what you need is to give mail the -- argument which lets you pass arguments straight to sendmail:
echo "message body" | mail -s "subject" firstname.lastname@example.org -- -F "Users Name" -f email@example.com