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

% Setzen der Absenderadresse
\setkomavar{fromaddress}{%
Hackspace Jena e.V.\\
Postfach 100 132\\
07701 Jena}
\setkomavar{fromname}{Hackspace Jena e.V.}
\setkomavar{fromemail}{office@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,
firstfoot=on,
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}

\setkomavar{firstfoot}{
\hrule
\smallskip{}
\parbox[t]{\linewidth}{\footnotesize
\begin{tabular}{llll}
  \usekomavar{fromname} & \textbf{Bankverbindung} & \\
  Postfach 100 132 & IBAN: DE55 8309 4495 0003 1839 12 & Inhaber: Hackspace Jena e.V.\\
  07701 Jena &  BIC: GENO DE F1 ETK & Ethikbank Eisenberg\\
\end{tabular}%
}%
}


\begin{letter}{zieladresse}

\setkomavar{subject}{Some subject}

\opening{Sehr geehrte Damen und Herren,}

Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam
nonumyeirmod tempor invidunt ut labore et dolore magna aliquyam
erat, sed diamvoluptua. At vero eos et accusam et justo duo dolores
et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est
Lorem ipsum dolor sit amet.Lorem ipsum dolor sit amet, consetetur
sadipscing elitr, sed diam nonumyeirmod tempor invidunt ut labore et
dolore magna aliquyam erat, sed diamvoluptua. At vero eos et accusam
et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea
takimata sanctus est Lorem ipsum dolor sit amet.Lorem ipsum dolor
sit amet, consetetur sadipscing elitr, sed diam nonumyeirmod tempor
invidunt ut labore et dolore magna aliquyam erat, sed diamvoluptua.
At vero eos et accusam et justo duo dolores et ea rebum. Stet clita
kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit
amet.Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed
diam nonumyeirmod tempor invidunt ut labore et dolore magna aliquyam
erat, sed diamvoluptua. At vero eos et accusam et justo duo dolores
et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est
Lorem ipsum dolor sit amet.Lorem ipsum dolor sit amet, consetetur
sadipscing elitr, sed diam nonumyeirmod tempor invidunt ut labore et
dolore magna aliquyam erat, sed diamvoluptua. At vero eos et accusam
et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea
takimata sanctus est Lorem ipsum dolor sit amet.Lorem ipsum dolor
sit amet, consete

\closing{Mit freundlichen Grüßen}

\end{letter}
\end{document}