I am building an app for Mac OS X that brings in email addresses from an Excel file.
Is there any method in the SDK that would allow me to check if an email is valid, e.g. a Hard Bounce? Something similar to using ping but for emails?
No, there is not.
The only way to test if an email address will bounce is to try sending it an email and see if it bounces. It isn't possible to do this directly from most desktop computers, as most residential ISPs block outbound SMTP, and there is no method in the Mac OS X frameworks to do so.