CakePHP: Has anyone ever seen email functionality inside a model of MVC?

DISCLOSURE: I am a CakePHP core developer, but my answers are my own. They are not shared/reviewed by any CakePHP team member before posting and only represent my personal opinion. Both are considered 'bad design'. I would suggest the use of 'events' in CakePHP. Furthermore, sending emails should be a worker's task and so the event should only push the job to a queue that can later be processed, thus moving email sending to the shell (not controller and definitely not model). Now, because I understand that some applications don't need the most advanced setups, the email could be sent directly from the event. This makes for well organized/structured code that can be easily tested.

Email functionality should not go into the model OR the controller. The functionality should be a separate service, an internal application API of sorts which can be called from absolutely wherever - model OR controller. Compartmentalization and independent components are key to the success of any big enterprise system.

Typically, the model encapsulates the data layer and nothing else. This can be problematic in some cases, e.g, if you have multiple controllers that each need to trigger the same e-mail logic. In small systems, moving that logic into the model itself is potentially fine, but the concept of "fat models" is not likely to scale well, as it breaks encapsulation. I generally encourage such logic to be encapsulated in an adapter (sometimes called a "mediating controller"). Your controllers now only talk to the adapter, which sends the e-mail and then calls into the model.

You are right. Email functionality should be implement in controller. As example if ( false !== doModelInstruction() ) { sendEmail() }. Model is dedicated stricte for database manipulation, nothing more.

It all depends on how you interpret MVC. In some cases it's perfectly fine to have email functionality in the Model. In others you need to have a different approach as suggested. It should never be in the controller, however. At least specifically in terms of CakePHP, it's good to have in the model if you understand the implications and your use and interpretation of MVC is not broken.