In the letter, the couple's public relations representative wrote it was "gravely concerning that an influential slice of the media" has printed "distorted, false or invasive" articles.
"There is a real human cost to this way of doing business and it affects every corner of society," the letter said.
"The Duke and Duchess of Sussex have watched people they know - as well as complete strangers - have their lives completely pulled apart for no good reason, other than the fact that salacious gossip boosts advertising revenue."
The BBC was told that the letter had been sent to the editors of the Sun, the Daily Mail, the Daily Mirror and the Daily Express newspapers.
The Daily Star, which was not specifically mentioned, is published by the same group that publishes the Mirror and Express titles.
The ban on engagement with the papers will mean that the couple's PR team will no longer even answer calls from the papers asking them to confirm whether claims made about the couple are true or not.
'Not avoiding criticism'
Outlining the new policy of "no corroboration and zero engagement" with all the publications that received it, the letter said the measure would also protect the couple's communications team "from the side of the industry that readers never see".
"This policy is not about avoiding criticism," the letter continued.
"It's not about shutting down public conversation or censoring accurate reporting. Media have every right to report on and indeed have an opinion on the Duke and Duchess of Sussex, good or bad. But it can't be based on a lie."
The letter said the couple will continue to work with other media and "young, up-and-coming journalists" to raise awareness of the issues and causes they care about.
As The Duke and Duchess of Sussex now settle into the next chapter of their lives and no longer receive any publicly funded support, we are writing to set a new media relations policy, specifically as it pertains to your organisation.
Like you, The Duke and Duchess of Sussex believe that a free press is a cornerstone to any democracy— particularly in moments of crisis. At its best, this free press shines light on dark places, telling stories that would otherwise go untold, standing up for what's right, challenging power, and holding those who abuse the system to account.
It has been said that journalism's first obligation is to the truth. The Duke and Duchess of Sussex agree wholeheartedly.
It is gravely concerning that an influential slice of the media, over many years, has sought to insulate themselves from taking accountability for what they say or print—even when they know it to be distorted, false, or invasive beyond reason. When power is enjoyed without responsibility, the trust we all place in this much-needed industry is degraded.
There is a real human cost to this way of doing business and it affects every corner of society.
The Duke and Duchess of Sussex have watched people they know—as well as complete strangers—have their lives completely pulled apart for no good reason, other than the fact that salacious gossip boosts advertising revenue.
With that said, please note that the Duke and Duchess of Sussex will not be engaging with your outlet. There will be no corroboration and zero engagement. This is also a policy being instated for their communications team, in order to protect that team from the side of the industry that readers never see.
This policy is not about avoiding criticism. It's not about shutting down public conversation or censoring accurate reporting. Media have every right to report on and indeed have an opinion on The Duke and Duchess of Sussex, good or bad. But it can't be based on a lie.
They also want to be very clear: this is not in any way a blanket policy for all media.
The Duke and Duchess of Sussex are looking forward to working with journalists and media organisations all over the world, engaging with grassroots media, regional and local media, and young, up-and-coming journalists, to spotlight issues and causes that so desperately need acknowledging. And they look forward to doing whatever they can to help further opportunities for more diverse and underrepresented voices, who are needed now more than ever.
What they won't do is offer themselves up as currency for an economy of click bait and distortion.
We are encouraged that this new approach will be heard and respected.