my ($subject, $message);
if ($old ne $curr) {
  $subject = 'Subject A';
  $message = 'Subject A message here';
} elsif ($var eq $job) {
  $subject = 'Subject B';
  $message = 'Subject B message here';
} else {
  $subject = 'Subject C';
  $message = 'Subject C message here';
}

my %mail = ( To      => 'mail@there.com'',
             From    => 'from@there.com',
             Subject => $subject,
             Message => $message,
           );
$mail{smtp} = $mailserv;
sendmail(%mail) || die "\nProblem! $Mail::Sendmail::error\n";