Is it possible to tell if an email was sent through a smartphone? Is there something marked in the email headers?
Mail from a 'normal' computer and mail from a smartphone is sent the same way (via SMTP).
Thus the short answer is: No.
The slightly longer answer is that a mail client is allowed to add extra header. Thus if a client adds "X-header: sent from my crackberry" then you can detect it. But allowed is not the same as required. There is no guarantee whatsoever that any such header gets set.