As a verb, this first name means to send mail free of charge
[DOC] [TLE] Frank | Definition of Frank by Merriam-Webster [PAR] The word frank comes from the name of the Franks, a West Germanic people who 
... means free or forthright, we get the verb frank, which means to mark mail 
with ... First Known Use: 1535 ... 2 : the privilege of sending mail free of charge.