Cost optimized email attachment download in a mobile device

A system and method for reducing data usage for wireless subscription plans. An email and an attachment are downloaded to a first device of a first recipient. An attachment is identified on the email by an attachment processing service that ensures that sharing from the first device is based on a credit policy. That there is more than one recipient for the email and attachment is determined. That a second device of a second recipient is in the vicinity of the first device is determined. Verification of the second device is established with an email fingerprint exchange handshake based on a fingerprint of the email for the second recipient that is computed from a hash of content of the email, an identifier of the attachment, and an email id of the second recipient. A second network is utilized to copy the attachment from the first device to the second device.