Inquiries are continuing to determine the nature of the substance found at the Alliance and Leicester office in Douglas, which led to a security operation in the town centre.
The office on Prospect Hill was evacuated and sealed off after an envelope containing white power was discovered on Friday morning.
It triggered a full turn out of the Island's emergency services and a section of the main road was closed for nearly two hours.
A criminal inquiry's been launched and specialist officers from Merseyside called in to analyse the substance.
Police say initial tests show there are no contaminaiton issues to either staff or the property.