Use a boolean variable to remember whether you found one or more newer files. After the loop this boolean variable tells you what you want to know. Since it is not strictly a boolean variable it also tells you how many newer files it found

...
my $newfilefound=0;
  $localtimenoformat=time;
for $file (@files) {
  $mdtmnoformat=$ftp->mdtm($file);
  unless ( ($localtimenoformat - $mdtmnoformat) > 3600 ) {
    $newfilefound++;
  }
}
if (not $newfilefound) {
  envia_mail();
}
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