Get post meta supposedly return string but array

Hi i have this code that should return string because the last parameter is true (according to the reference here http://codex.ww.wp.xz.cn/Function_Reference/get_post_meta). However i keep getting array in return.

$email_list = get_post_meta($cpnid, 'customer_email', true);

I should be getting comma separated value like this
[email protected],[email protected],[email protected]

but i get a word “Array” instead…

Thanks for your help.