The MHA, Delhi Police later said nothing was found after thorough checking, adding that an investigation was underway. Delhi Police Crime Branch Special CP Ravinder Yadav said apart from schools, these emails were received by some hospitals also.

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Delhi Public School in Dwarka, RK Puram, Noida and Vasant Kunj, Mother Mary's School in East Delhi Mayur Vihar, and Sanskriti School in Chanakyapuri were among the over 200 schools that received bomb threats via email on Wednesday. A school in Lucknow also reportedly received a threat later in the day.

Origin of Mail, ISISI Link 

Officials said the initial probe suspected a "deeper conspiracy" by a terror group during the Lok Sabha elections, adding that there is suspicion that the threat mail was sent by an ISIS module. The Delhi Police's anti-terror unit special cell has traced the domain of e-mails to Russia and it is suspected to have been formed with the help of the dark web -- an encrypted online content that allows individuals to hide their identity and location from others.

The National Investigation Agency may also take up the probe since the role of a terror group is suspected and the "conspiracy" angle may lead to a pan-India investigation, an official said.

What Was Written In The Mail 

According to a police officer, the e-mail ID from which the threat was sent is '[email protected]'. Sawarim is an Arabic word extensively used by the terror outfit Islamic State (IS) in their propaganda videos over the past several years, the official said.

"Kill them wherever you meet and drive them out of the places from which they drove you. There are many explosive devices in the school...," reads the identical email sent to all schools.

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Reports also said that it took some time for the police to trace the email's origin as it was sent using a virtual private network (VPN) that routed and rerouted data through foreign servers. The police managed to narrow down on the internet protocol (IP) address - a unique identifier - after retracing the VPN traffic and found the source of the email, sources cited in an NDTV report said.