Hello
I have similar problem.
“Postman: wp_mail has been declared by another plugin or theme, so you won’t be able to use Postman until the conflict is resolved.” error in the admin panel. So, I’ve read this thread and figured out the compatibility problem. And I’ve figured out what this plugin is (our payment gateway).
It really was declaring “require_once( ABSPATH . “wp-includes/pluggable.php” );”
I’ve found it and deleted, and no other files in the plugin have it. But, I still have the same error in the admin panel. When I disable payment gateway plugin, Postman smtp works perfectly.
Do you have any other ideas what may cause the compatibility issue?
Thanks.
