By comparing the “hash values” it should show if the files have been changed.
Computer files have hash values.
What is a “hash value”? A judicial guide defines “hash value” as:
“A unique numerical identifier that can be assigned to a file, a group of files, or a portion of a file, based on a standard mathematical algorithm applied to the characteristics of the data set. The most commonly used algorithms, known as MD5 and SHA, will generate numerical values so distinctive that the chance that any two data sets will have the same hash value, no matter how similar they appear, is less than one in one billion. ‘Hashing’ is used to guarantee the authenticity of an original data set and can be used as a digital equivalent of the Bates stamp used in paper document production.”
In forensic work such as pedophile computer searches, they just screen for the known hash values of common child porn photos rather than opening all the pics.
They should be able to compare the hash values of the delivered emails with the original back up values.