\documentclass[12pt]{letter}
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\usepackage{hyperref}
\usepackage{graphicx}
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\begin{document}

\address{
C.N. Yang Institute for Theoretical Physics \\
State University of New York at Stony Brook \\
Stony Brook, NY 11794-3840\\
phone: 631-632-mine\\
fax: 631-632-7954\\
email:me@insti.physics.sunysb.edu}

\signature{%\vskip-.5in\includegraphics{signature}\vskip.1in
Me\\
Professor}

\newcommand{\writeletter}{

Letter

\closing{Sincerely,}

\end{letter} }

\begin{letter}{
Prof. Whoever\\
wherever}

\opening{Dear Prof.\ Whoever,}

\writeletter

\end{document}
