The German news magazine Der Spiegel cited the Snowden documents in a story posted Sunday.
Der Spiegel says the documents describe an operation dubbed "Flat liquid" that claim to have accessed Mexico's "presidencia" domain, which was also purportedly used by members of Calderon's Cabinet.
Harvard's Kennedy School of Government, where Calderon is now a fellow, did not respond to emails requesting comment.
Earlier, a document dated June 2012 indicated the NSA had read current Mexican President Enrique Pena Nieto's emails before he was elected.
Pena Nieto has said that would be an illegal act if it occurred, and his administration has demanded an investigation.
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