\documentclass{ppex}
\nonstopmode
\AtEndDocument {\end {fmffile}} \AtBeginDocument {\begin {fmffile}{ftmp}}
\usepackage {feynmp}
\pagestyle{empty}
\setlength\textwidth{207.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {feynmp}
\begin{fmfgraph*}(100,70)
  \fmfleft{em,ep}
  \fmf{fermion}{em,Zee,ep}
  \fmf{photon,label=$Z$}{Zee,Zff}
  \fmf{fermion}{fb,Zff,f}
  \fmfright{fb,f}
  \fmfdot{Zee,Zff}
\end{fmfgraph*}
\end{document}