\documentclass[12pt]{letter}

% ---------------------------------------------------------------
% Packages
% ---------------------------------------------------------------
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[
  a4paper,
  top=2.5cm, bottom=2.5cm,
  left=2.5cm, right=2.5cm
]{geometry}
\usepackage{parskip}   % space between paragraphs instead of indent

% ---------------------------------------------------------------
% Sender information  ← fill these in
% ---------------------------------------------------------------
\address{
  Philipp Waibel\\
  % Your Company / Department \\
  Zelgistrasse 2\\
  8266, Steckborn\\
  % Country
}

\signature{
  Philipp Waibel\\
  % \textit{Job Title} \\
  % \textit{your.email@example.com} \\
  % \textit{+00 000 000 0000}
}

% ---------------------------------------------------------------
\begin{document}

\begin{letter}{%
  Mobiliar \\
  % Recipient Company \\
  Wilerstrasse 12 \\
  8370, Sirnach\\
  % Country
}

% --- Opening -----------------------------------------------
\opening{Dear Mr./Ms./Dr.~Last Name,}

% --- Subject line (optional) --------------------------------
\textbf{Re: Subject of the Letter}

\vspace{0.5em}

% --- Body ---------------------------------------------------
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Phasellus at dignissim ipsum, nec tincidunt nulla.
Donec pretium neque id turpis blandit, a condimentum enim sodales.

Sed ut perspiciatis unde omnis iste natus error sit voluptatem
accusantium doloremque laudantium, totam rem aperiam eaque ipsa quae
ab illo inventore veritatis et quasi architecto beatae vitae.

At vero eos et accusamus et iusto odio dignissimos ducimus qui
blanditiis praesentium voluptatum deleniti atque corrupti quos dolores
et quas molestias excepturi sint occaecati cupiditate non provident.

% --- Closing ------------------------------------------------
\closing{Yours sincerely,}

% --- Optional enclosures / CC -------------------------------
\encl{Enclosure 1, Enclosure 2}
% \cc{Name of CC Recipient}

\end{letter}
\end{document}