Security around the heritage building was beefed up immediately after the mail was received at the police headquarters at nearby Lalbazar and a search was conducted by Kolkata Police officers.
Senior Kolkata Police officers along with the bomb squad personnel, sniffer dog squad rushed to the building, which was vacated soon after as part of security measure.
"We are looking into who has sent the mail. We are not taking any chances and are conducting search operations there in the Writers Buildings," a senior officer of Kolkata Police said.