Where in my architecture should external interaction be handled?

The current architecture of my project is as below...

• Presentation (ASP MVC & View Models)
• Business Logic (Services & Domain Models)
• Data Access (Repositories & Units of Work & Entity Models)

Currently both my business logic and access to external sources (i.e. SMS, Email, Verifying Recaptcha) are handled by services, so you have PersonService sat alongside EmailService. The Person service is unit testable where as the EmailService is not and them sitting at the same layer does not seem right.

Does anyone have any better suggestions for where this should go?