Permissions for mail policies

I created a patch for his, see attachment

Thanks it's a good idea.

Drupal.org now requires merge requests instead of patches. There is a new 2.x branch now and all fixes should be against that. There is now a separate module for mailer policy so your fix makes a lot of sense.

Added fork/MR the 2.x branch

Thanks I've taken a look.

Please can you give me any example in Core where a config entity has an access control hander and complex permissions like this?

The IS says

Some roles should be able to change mail templates only

A possible simpler solution: have a single permission for changing mailer policy, separate from any other permission of this module.