Police said they were aware of several reports of these letters across Auckland and were investigating.
The hand-written cards have been sent to residents in West Auckland, the North Shore, South Auckland and Ellerslie.
Recently, a woman who lives in the Waiuku area shared a post revealing she found a "with sympathy" card in her mailbox and thought it was a "sick joke" as she hadn't suffered a loss.
Inside the card, a person has handwritten that "this message has come to me from angels who are with you. We wish you to know that your daughter is with you in spirit".
"Your daughter is very well and she would like you to be happy to know that you will meet again in heaven some day."
The resident said she shared the letters to make people aware in case they have been put in a similar situation.
"We found this misguided card in our letterbox. After sharing it on our local grapevine there seems to be a few others who have received similar cards.
"Someone else received a similar message, nearly identical words and handwriting, on the North Shore a few months ago.
"By sharing it I'm hoping it can seem less personal to anybody else unfortunate enough to have been in the firing line and fingers crossed it will stop whoever is writing them."
A woman from Clevedon revealed that she got the same card a few weeks ago with the same handwriting.
"Looked like it was hand delivered and the message was kind of similar, eg meet again in heaven.
"We binned it. Thought it was kind of weird but didn't dwell on it. Looks like someone may have too much free time perhaps?"
Another woman said her sister, who lived on the North Shore, was given one of the cards earlier in the year.
"It really upset her even though she hadn't lost a child.
"It was in a stamped enveloped but hand delivered from memory as had no stamp marks."
The Facebook post caused some controversy, with some agreeing it was a "sick joke".
"If I had to receive it I would be so distraught, one person wrote.
Another agreed: "How upsetting for you guys. I hope it is a case of mistaken identity, otherwise it's just evil."
"If it's been hand delivered it's not hard for the person to have gone and had a look at mail from their letterbox for their name. Some creepy ass people in this world," one said.
However, others believed it may have been given to her by mistake.
"Don't mean to intrude but what if someone genuinely means this? There are psychics out there and it seems like a nice message to me? Not a sick joke at all," one wrote.
Another agreed: "I don't actually see what's wrong with it ... nothing in the card is threatening or malicious ... and it seems like they are trying to be comforting.
"Probably the person who delivered it put it in the wrong box."
