Can I access headers of all the emails sent within one "Google Apps" domain?

I would like to create a l开发者_如何学运维ive visualization of all the mail communication happening within one "Google Apps" domain used in my organization.

Is there any API which I can use to get a live callbacks, or at least some API which I can pull periodically in order to get headers of all the emails sent within the organization?

Use the Email audit API:

http://code.google.com/googleapps/domain/audit/docs/1.0/audit_developers_guide_protocol.html

Please remember Email Audit API can be used only for lawful purposes in accordance with your Customer Agreement. There is currently no other way to do what you need.