I thought the problem was the writing to a file handle bound to a string ref (\*BODY), so I tried it with IO::String, but it still didn't work:

#!/usr/bin/perl

use strict;
use IO::Tee;
use IO::String;

my $email_body;
my $tee = IO::Tee->new(\*STDOUT,new IO::String($email_body));   # crea
+te a new tee object and attach STDOUT and the email$
die $! unless $tee;
$tee->autoflush(1);

my ( $check_description,$check_result,$severity_w );
my $VERSION = 10.0;
my $host = "test";
format HEADER =
____v@<<<< @<<<<<<<<<<<_______________________________________________
+______________________________________________
$VERSION, $host

 Description                                                          
+               Check Result - Status-Severity
______________________________________________________________________
+______________________________________________
.
format FAIL =
   @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< @>>>>>>>>>>>>>>>>>>>>>>>>>>>
+>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>  -ERROR-@>
$check_description,$check_result,$severity_w
.
format STD =
   @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< @>>>>>>>>>>>>>>>>>>>>>>>>>>>
+>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
$check_description,$check_result
.

select STDOUT;
$^ = 'HEADER'; # set the top of page format
$~ = 'STD';

$check_description = "desc";
$check_result = "result";
$severity_w = "9";

write;

print "EMAIL BODY:\n\n$email_body\n";
exit;
[download]

Had to learn something about formats, I think everything is correct except IO::Tee doesn't handle a string filehandle properly. The formats output fine if selecting STDOUT. SSF