\documentclass{standalone}
\usepackage{feynmp-auto}

\begin{document}
    
    \begin{fmffile}{diagram}
        \begin{fmfgraph*}(120,80)
            \fmfleft{i1,i2}
            \fmfright{o1,o2}            
            \fmf{fermion}{i1,w1,w2,i2}
            \fmf{fermion}{o1,w3,w4,o2}
            \fmf{photon}{w1,w3}
            \fmf{photon}{w2,w4}
        \end{fmfgraph*}
    \end{fmffile}

\end{document}