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

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "addressee":
   accepter, acquirer, artist-in-residence, audience, auditor,
   beholder, communicator, consignee, correspondent, denizen, dweller,
   getter, habitant, hearer, holder, house detective, incumbent,
   inhabitant, inhabiter, inmate, inpatient, intern, letter writer,
   listener, live-in maid, locum tenens, looker, obtainer, occupant,
   occupier, payee, pen pal, procurer, receiver, recipient,
   residencer, resident, resident physician, residentiary, resider,
   sojourner, spectator, taker, tenant, trustee, viewer, writer



The Free On-line Dictionary of Computing (30 December 2018):

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)