The e-mail containing a threat to President APJ Abdul Kalam is believed to have originated in Indore and special teams are trying to locate the computer used to send it, police sources said on Friday.
Preliminary information about the e-mail, which was sent to the President's official website on July 19, indicated it originated from Indore, they said.
Special teams led by senior officials are trying to locate the computer from which it was sent, they said.
Police teams have fanned out across the city and a close watch is being maintained on cyber cafes and public computers, the sources said.
It is still not clear whether the email was simply aimed at creating a sensation as in the case of three other e-mails about bombs sent from Madhya Pradesh to newspapers and TV channels after the Mumbai blasts, they said.