Disclosed herein are methods and systems for monitoring and detecting changes in files attached to incoming emails. In one embodiment, if files are attached to an outgoing email, the change service uniquely tags each of the attached files and optionally stores local or remote copies of the tagged files. Additionally, in embodiments, the change service monitors and intercepts incoming emails. If files are attached to an incoming email, the change service identifies whether the files are tagged in a manner unique to the compare service. The change service then matches uniquely tagged files in the incoming email to corresponding files previously tagged by the change service. The change service then compares the two documents and generates reports that identify changes in the received document in relation to the transmitted document. Further, in embodiments, the change service provides visual indicators of the changes within the email application.