Koolhaas, Rem
Elements
Venice, Marsilio
Buku Referensi
Webster's guide to business correspondence
Merriam-Webster, Inc., 1988
Buku Teks
Bowman, Joel P.
Effective business correspondence
Harper & Row Publishers, 1979
Buku Referensi
Wildermuth, J.R.
English hotel correspondence
Ecole Hotellere, 1978
Buku Teks
Bouwens, C.
English Commercial correspondence
Persatuan Tenaga, 1957
Buku Teks