I've been a fan of MIME::Lite and functional ternary expressions for awhile, so here's my take on it (untested, but I usually get these right on the first shot):

use strict;
use MIME::Lite;

my $old           = 'Foo';
my $curr          = 'Foo';
my $from          = 'from@there.com';
my $to            = 'mail@there.com';
my $subject       = 'Subject C message here';

# You could nest one more ternary in here for
# '$var eq $job'
$old ne $curr 
       ? $subject = 'Subject A message here' 
       : $subject = 'Subject B message here';

my $msg = MIME::Lite->new( 
          From    => $from,
          To      => $to,
          Subject => $subject,
          Data    => "Here's the message body you wanted",
          Type    => 'text/plain'
);

# You'd want $msg->send; though, of course
print $msg->as_string;
[download]