Well, something like this should do the trick:

sub print_details {
  my $fh = shift;
  print $fh "We have recieved your order for a $pizza_size pizza with 
+";
  pizza_toppings();
 } 

open my $sendmail, "| /usr/sbin/sendmail -t" or die ("no sendmail??");
[...]
print $sendmail "Subject: ...\n\n";
print_details($sendmail);
close $sendmail;
[download]

Just make sure you call print_details everywhere with a filehandle as argument.
If this doesn't help you, read the docs I pointed you to, it's all there. ( and here too: open, perlfaq filehandle )

regards,
tomte

---