SendMyEmail.pm
SendMyEmail/defualt_email.tt

# This is what I would like to do.
package SendMyEmail;
sub new {
    my ($self, $template) = @_;
    $template ||= $dir_of_SendMyEmail .'/SendMyEmail/default_email.tt'; # ??
}

my $DEFAULT_TEMPLATE;
BEGIN {
	$DEFAULT_TEMPLATE = __FILE__;
	$DEFAULT_TEMPLATE =~ s,.pm$,/default_email.tt,;
}

package Foo::Bar;

use Cwd qw(abs_path);
use File::Basename qw(dirname);

sub module_dir { abs_path(dirname(__FILE__)) }

1;

use Foo::Bar;

print Foo::Bar->module_dir, "n";

## load the module
use Data::Dumper;

## output full path to Data::Dumper module loaded
print $INC{'Data/Dumper.pm'};

## see which module was loaded (if you have multiple folders with same modules)
print Dumper(%INC);

perlwhere() {
    perl -wle'eval "require $ARGV[0]" or die; ($mod = $ARGV[0]) =~ s|::|/|g; print $INC{"${mod}.pm"}' $1
}