\documentclass[fontsize=12pt,paper=a4,DIN]{scrlttr2}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}

% Setzen der Absenderadresse
\setkomavar{fromaddress}{%
Hackspace e.V. 
Postfach xyz
077xx Jena}
\setkomavar{fromname}{Hackspace Jena e.V.}
\setkomavar{fromemail}{kontakt@hackspace-jena.de}
\setkomavar{place}{Jena}
\setkomavar{signature}{Irgendein Vertreter}

%KOMAscript schön machen
\KOMAoptions{headsepline,%
pagenumber=topright,%
fromalign=center,%
fromrule=on,%
foldmarks=off,%
backaddress=off,%
firstfoot=off,
locfield=wide,%
enlargefirstpage=on,%
parskip=half%
}

\addtokomafont{fromname}{\Large}
\makeatletter
\@setplength{locwidth}{.5\textwidth}
\makeatother

\setkomavar{location}{\raggedleft
  \usekomavar*{fromemail}\usekomavar{fromemail}\\
  \usekomavar*{fromphone}\usekomavar{fromphone}\par
}


\begin{document}

\begin{letter}{zieladresse}

\setkomavar{subject}{Some subject}

\opening{Sehr geehrte Damen und Herren,}


\closing{Mit freundlichen Grüßen}


\end{letter}
\end{document}
