I'm having the same issue with lumen 5.2.4. The response is Class 'Mail' not found. Thanks so much!

I had issues with this as well. I ended up solving the error you mentioned by redirecting the namespace that was originally "Illuminate/Contracts/Mail" as outlined in some of the documentation I found to "Illuminate/Mail/Mailer" and was able to successfully get an instance of Mailer to use. However, the only thing that accomplished was throwing another BindingResolutionException when trying to instantiate the Swift_Transport interface inside the Swift_Mailer class. Still digging further down the rabbit hole. Good luck!