The Indian Mujahideen module, which sent the terror mail claiming responsibility for the Varanasi blast, had hacked into a broadband Internet connection of a Navi Mumbai resident.
Police sources said that the Wireless Fidelity (WiFi) that was used to send the five-page email was traced to a house in sector 17, Vashi in Navi Mumbai.
The house owner's insecure WiFI was hacked into, the sources said, adding the logger of the router has been disabled so there no trace of who logged into it and hacked it.
The police questioned the man and believe that he is innocent.
Mumbai Police had picked up father-son duo for questioning here in connection with the e-mail sent by banned terror group Indian Mujahideen.
The terror mail was quickly traced to the residential complex in Navi Mumabi. Indian Mujahideen had claimed responsibility for yesterday's blast at a crowded bathing ghat in Varanasi that left a child dead and 37 others injured.
Terrorists of Indian Mujahideen have been using unsecured WiFi connections for sending mails to media houses within minutes of blasts taking place.
The e-mail ID used were from gmail. The mail was written on December six and the account has been accessed rarely, the sources said.