Japanese media reports said earlier the e-mail address was provided by a hostage's wife who received a message from IS back in November 2014, saying they were holding her husband captive.
The two hostages held by IS fighters at an unknown location are Haruna Yukawa, the founder of a private security firm, and Kenji Goto, a freelance journalist, who were abducted in Syria last year. They first appeared in video footage that was posted on the Internet by IS.
Government spokesperson Yoshihide Suga, told reporters they had been exploring the possibility of contacting the militants but had been unable to so far.
On Tuesday, Islamists threatened to execute the hostages in three days' time, unless Japan pays them a ransom of $200 million. This sum matches the amount of money promised by Prime Minister Shinzo Abe as a nonlethal aid package to countries fighting the IS group.
Reports transpired in the Japanese media on Thursday that Abe had said Japan would not pay ransoms to terrorists, in a phone conversation with UK Prime Minister David Cameron. Abe also said earlier his country would not give up its plans to assist the fight against IS.