The Collaborative International Dictionary of English v.0.48:

Addressee \Ad`dress*ee"\, n.
   One to whom anything is addressed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

addressee
    n 1: one to whom something is addressed

The Free On-line Dictionary of Computing (19 January 2023):

addressee

    One to whom something is addressed.
   E.g. "The To, CC, and BCC headers list the addressees of
   the e-mail message".  Normally an addressee will eventually be
   a recipient, unless there is a failure at some point (an
   e-mail "bounces") or the message is redirected to a
   different addressee.

   (2000-03-22)