function! s:KillSignature() abort
    call cursor(1, 1)
    call search('^[>|] \?-- \?$')
    if getpos(".")[1] != 1
        normal d}
    endif
endfunction

autocmd BufRead /tmp/mutt-* call s:KillSignature()
autocmd BufRead /tmp/mutt-* setlocal textwidth=72
autocmd BufRead /tmp/mutt-* setlocal commentstring=>%s
autocmd BufRead /tmp/mutt-* silent %substitute /^> */>/e | set nohlsearch