I understand this is found in the 'Edit' option for the profile we would like to change, however when we click on 'Edit', we can alter the upper options via checkboxes, but are presented with "You cannot modify other permissions for this profile." for the lower section which contains 'General Permissions' and ultimately the 'Mail Send' option.

We have tried to access these options with administrator permissions, but still can't find the proper access to disable this.

What is the best way to disable this mail send option?