I would like to remove the middle foldmark, just leaving the upper and lower: I think m should do it but it is not working for me.
\documentclass[a4paper, foldmarks=true, foldmarks=mBT]{scrlttr2}
\setkomavar{fromname}{my name}
\setkomavar{fromaddress}{my house \\ my address}
\begin{document}
\begin{letter}{address}
\opening{Dear all,}
This is a letter.
\closing{Yours faithfully,}
\end{letter}
\end{document}

