fix(mail): refactor(mail): Remove Mailgun references from PlatformService. Update keywords, error messages, and documentation to use MTA exclusively.

ts/mail/services/classes.apimanager.ts

@@ -69,10 +69,10 @@ export class ApiManager {
           return status;
         }
         
-        // For Mailgun, we don't have a status check implementation currently
+        // Status tracking not available if MTA is not configured
         return {
           status: 'unknown',
-          details: { message: 'Status tracking not available for current provider' }
+          details: { message: 'Status tracking not available without MTA configuration' }
         };
       })
     );