\LoadLetterOption{DIN}
\newkomavar{transaction}
+\newkomavar[\lieferschein{}~\nr]{delivery}
+\newkomavar[\angebot{}~\nr]{quote}
\usepackage{geometry}
\medskip
\begin{tabularx}{\linewidth}{@{}l<{:}>{\raggedright\arraybackslash}X@{}}
\usekomavar*{date}&\usekomavar{date}\\
+ \ifkomavarempty{myref}{}{
+ \usekomavar*{myref}&\usekomavar{myref}\\
+ }
\kundennummer&\usekomavar{customer}\\
+ \ifkomavarempty{yourref}{}{
+ \usekomavar*{yourref}&\usekomavar{yourref}\\
+ }
+ \ifkomavarempty{delivery}{}{
+ \usekomavar*{delivery}&\usekomavar{delivery}\\
+ }
+ \ifkomavarempty{quote}{}{
+ \usekomavar*{quote}&\usekomavar{quote}\\
+ }
\ansprechpartner&\usekomavar{fromname}
\ifkomavarempty{fromphone}{}{\\\textTelefon&\usekomavar{fromphone}}
\ifkomavarempty{fromemail}{}{\\\textEmail&\usekomavar{fromemail}}