[Tex/LaTex] Indent first paragraph of letters

indentationletters

In this thread it is explained that package indentfirst interacts with section headings, which a letter does not have.

So, how can I get L(u)aTeX to do that, i.e. indent the first paragraph of a letter? Moreover, in my letters none of the paragraphs are getting indented, so I could also use help with that. (It happened in several letters, with different options / packages, so I'm assuming it's supposed to be that way — and that's why I did not provide a minimal working example). Thanks in advance!

EDIT: As requested, here's a minimal example:

\documentclass[a4paper,12pt]{letter}

\usepackage{indentfirst}

\date{February 31, 2013}
\address{ 22nd Baking Street }
\signature{Your Truly's Name}

\begin{document}
\begin{letter}{ R. MaDillo  }
\opening{Dear Dr. R. MaDillo,}
 Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec bibendum
 suscipit odio, id dapibus ipsum placerat vitae. Quisque vitae magna vel ante
 semper dapibus sit amet eu elit. Fusce cursus sodales eros, non porta urna
 bibendum et.

 Vivamus dictum pretium iaculis. Suspendisse eros ligula, laoreet elementum
 lobortis vel, blandit tincidunt enim. Aenean eget augue dolor. Sed ut magna
 nec nulla euismod pharetra. Proin diam turpis, tincidunt et fermentum id,
 porta ut nulla.

 \closing{Yours sincerely,}
 \end{letter}
 \end{document}

Best Answer

You could try to

\setlength{\parindent}{0.5cm}

but you probably would like to put this command after the \opening{} so as not to indent this as well.