\documentstyle[12pt,a4,physhead]{letter}
\signature {name} 
\address{additional address}
%\makelabels % generate labels after all the letters
\begin{document}

\begin{letter}{%
Dr. Who\\
Where}
\opening{Dear Who,}

% message text

\closing{Sincerely,}
\end{letter}
\end{document}