If your webserver is running an OS that supports it then you could use fork something like :

#!/usr/bin/perl -w

use CGI qw(redirect);
use strict;

$| = 1;


if (my $pid = fork)
{
     print redirect 'http://www.whatever.com';
}
else
{
    close STDIN;
    close STDOUT;
    
    # do your mail sending here
}
[download]

Closing STDIN and STDOUT is important so the server knows to close the connection to the browser

/J\