\documentclass[10pt,a4paper,twoside,onecolumn]{letter}

\usepackage{units}
\nonstopmode

\usepackage{graphicx}
\usepackage{lipsum}
\usepackage{tabularx}
\usepackage{lmodern}

\newcommand{\CO}{{\nicefrac{\raisebox{.2em}{\textsc{c}}}{\raisebox{-.3em}{\textsc{\kern -.1em o}}}}}

\begin{document}
\makelabels
\fontfamily{lmr}\selectfont
\begin{letter}
\address{%
    \ttfamily
\footnotesize
\parbox{0.5\linewidth}{%
\begin{tabular}{lr}
Hans Thomas {\scshape Reiser} \hfill ({\scshape cdcr} {\ttfamily\textnumero\ {\scshape g}31008}) \\
California Health Care Facility ({\scshape chcf}) &\\
\CO\ Dept. of Corrections \& Rehabilitation &\\
{\scshape usps PO} Box \textnumero 213040 &\\
Stockton, {\scshape ca} 95213+9040 &\\
United States of America &\\
\end{tabular}
}
}
\hspace {1em}
\vline
\hspace {1em}
\returnaddress{%
\ttfamily
\footnotesize
\parbox{0.5\linewidth}{%
{
\begin{tabular}{lr}
{\scriptsize {\itshape Be this letter undeliverable, return to}} &\\
Fredrick R. {\scshape Brennan} &\\
Modular Font Editor {\scshape k} ({\scshape mfek}) Fndn. &\\
\textnumero597\textsuperscript{\underline{A}} North Raleigh Avenue &\\
Atlantic City, {\scshape nj} 08401+1081 &\\
United States of America &\\
\end{tabular}
}
}
}

\opening{Dear Mr. Reiser,}

I am sorry to hear that one of your letters to me was lost.

Indeed, due to multiple problems with unit 597D, I was moved to 597A. I am very surprised that the Post Office did not simply forward the mail to the right address, but I suppose it cannot be helped.

I hope this letter reaches you without any problems this time, and if you wish to write me a longer letter again, I would be happy to receive it at 597A.

\closing{Sincerely,
\vspace{3em}
\signature{Fredrick R. {\scshape Brennan}}
}

\end{letter}
\end{document}

