Police are appealing for anyone who receives one of the vexatious letters to report it.

So far, reports have been made by a property owners at Dubbo, Walgett and Peak Hill.

The letter says to 'stop your whinging'.

"It is not Australia's problem that your farm is experiencing drought," it says.

The letter then goes on to tell the recipient "if you cannot handle it, go kill yourself".

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Police said initial inquiries indicate the letters are being hand-delivered to mailboxes. They urge victims to photograph and preserve the letters and envelopes before making a report to their local police station.

NSW Police Force Rural Crime Prevention Team state coordinator Detective Inspector Cameron Whiteside said the letters were "downright disgraceful".

"It is extremely important that these letters are not over-handled, both in a physical sense and by not disclosing information to fellow members of the public which may impact the investigation," he said.

"Victims should report the matter to local police in a very timely manner in order to increase our chances of resolving the nature of these letters."

"Anyone who has received a similar letter is encouraged to contact their local police station and report the matter."