Ottawa police are investigating after dozens of people in the city have complained about receiving threatening letters by mail at their home address that begin "I know where you live."

Police say in most of the cases, though not all, the hand-written address on the envelope is specifically naming one of the residents.

The letter found inside is a photocopy of a hand written note on an 8½ x 11 sheet of paper, and makes death threats to the reader and family.

The letter threatens, but does not attempt to extort money, said police spokesperson Const. Marc Soucy.

Stamp mark from Calgary

To date, Ottawa Police has received 27 complaints about similar letters since February.

Police say the stamp mark for the letter is from Calgary. Soucy declined to say whether Calgary police had been contacted, but said police are exploring every avenue in the investigation.

Police said the letter is being mass-distributed in the Ottawa area.

"We're a bit concerned those letters are circulating throughout the city and we're asking people if they've received such letters to let us know," Soucy said.

Anyone who receives a letter should avoid over-manipulating the letter and put it aside in a container — like a sealable freezer bag — to preserve the forensic evidence, and then contact police.

"We may be able to find fingerprints on the letters," Soucy said.

Police said they have not found any links between the recipients who received the threatening letter.

'A very horrifying death threat'

Ottawa resident Vicky Smallman, who received a letter on Monday, said the experience has been "extremely unsettling".

"It was a very horrifying death threat against me and a threat of violence against my family," she said.

apparently I am not the only person in Ottawa who received a death threat via the mail this week. If you are one of them, let me know. —@offhandremarks

Smallman said the one-page letter did not explain why she was being singled out, but she agreed to have her name shared with other victims so police could investigate possible connections. Smallman said the one-page letter did not explain why she was being singled out, but she agreed to have her name shared with other victims so police could investigate possible connections.

Since receiving the letter, Smallman said she has become more mindful and her family has taken steps to ensure their safety.

Vicky Smallman says she's become more mindful about her personal safety since receiving the threatening letter in the mail. (Supplied)

"We did a little safety audit around the house. [We] told the school that we had received a letter, had a discussion with our kids about safety."

Police are asking anyone who has received the letter, or has information about it, to contact the west criminal investigations unit at 613-236-1222, ext. 2666. Anonymous tips can be submitted by calling Crime Stoppers toll-free at 1-800-222-8477 (TIPS).