based on the scrlltr2 class. Address and location field and header were manually set to comply to the parameters of DIN5008A (small letter head)
% Letter template which should agree largely with DIN5008A https://de.wikipedia.org/wiki/DIN_5008
%
% Till Blaha 2023, Creative Commons
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Configuration
% According to DIN5008A, the height of the right-hand location field can vary between 40 and 75mm
% you can set this value accordingly, if you need more vertical space in that field
\newcommand{\mylocheight}{40mm}
% show foldmarks?
\newcommand{\showfoldmarks}{on} % on or off
% include the preamble
\input{preamble.tex}
%%% uncomment these 2 lines to make sure the boxes for address and location are not overrun
\LoadLetterOption{visualize}
%\showfields{head,address,location,refline,foot}
%%%%%%%%%%%%%%%%%%%%%%%%%% Content %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%
% Sender Variables %
%%%%%%%%%%%%%%%%%%%%
\setkomavar{fromname}{John Doe}
\setkomavar{fromaddress}{Freedom Drive 1960\\12345 City\\Country}
\setkomavar{fromphone}{+31 6 123 456 78}
\setkomavar{fromemail}{email@example.com}
\setkomavar{backaddressseparator}{\ \textperiodcentered \ }
\setkomavar{signature}{\hspace{5mm}\includegraphics[scale=1]{Signature}\\John Doe} % with scanned signature
%\setkomavar{signature}{\vspace{10mm} \\ John Doe} % without scanned signature
\setkomavar{place}{Some City}
\setkomavar{date}{\today}
\setkomavar{enclseparator}{: }
%%%%%%%%%%%%%%%%%%%%%%%%
% Letterhead variables %
%%%%%%%%%%%%%%%%%%%%%%%%
\setkomavar{letterheadsubtitle}{Aerospace Engineer}
%%%%%%%%%%%%%%%%%%%%%%
% Location Variables %
%%%%%%%%%%%%%%%%%%%%%%
\setkomavar{location}{
\newline\vspace{-18pt}% no idea why this hack is needed to align the table to the left
\begin{tabbing}
\hspace{35mm} \= \hspace{25mm} \= \kill % Spacing within the block
Reference Number: \> 123456789\\
Client Number: \> 202012345\\
Telephone: \> \usekomavar{fromphone}\\
Email: \> \usekomavar{fromemail}
\end{tabbing}
}
\begin{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Addressee %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{letter}{%
Addressee \\
Address line 1 \\
Address line 2 \\
Address line 3 \\
1234 AB Stad \\
les Pays-Bas
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Start of Actual Content of the Letter %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setkomavar{subject}{Letter of Motivation supporting my \LaTeX{} Template}
\opening{To whom it may concern,} % 100 words
\lipsum[1-4]
\vspace*{5mm}\textbf{Subsection Headline}
\lipsum[5]
\closing{Met vriendelijke groet,}
%%%%%%%%%%%%%%%%%%%%%%%
% Enclosures %
%%%%%%%%%%%%%%%%%%%%%%%
\encl{\textit{Proof (2 pages),\\ More Proof (7 pages)}}
%%%%%%%%%%%%%%%%%%%%%%%
% End of Tex Document %
%%%%%%%%%%%%%%%%%%%%%%%
\end{letter}
\end{document}