google app engine email attachment: download it to file system
You cannot write a File to your web application directory in App Engine.
Possible choices for you are:

Save the content in the Datastore.
Use the Blobstore
Use the Google Storage facility.

Alternately, you might want to post the content away to an external server that can store the data, either your own or some 3rd party like Amazon S3.
I am able to receive an email to app engine. I see the data in an attachment is payload base64 encoded data. Can I download the attachment as it is to file system without processing it or without storing it to blobstore?