A Sydney man's manifesto inciting people to "reclaim Australia" through lethal violence included death threats against Indigenous people, Invasion Day protesters and Muslims.

Raymond John Brookes mailed the four-page document to Sydney's largest mosque in Lakemba and independent Western Australia senator Fatima Payman in January.

Titled, "V for Vendetta", the often letter called for 'revenge' against Aboriginal people and Torres Strait Islanders, Muslims, the Labor Party, the Greens and "socialist" journalists at the ABC, SBS and the Guardian.

The Belmore resident called for anyone who protested during Invasion Day rallies to be "beaten to death" in the street.

"You must do your bit for Australia," the 70-year-old wrote.

He sent two letters to Lakemba Mosque, one addressed to the Mullah and the other to the Australian Muslim Advocacy Network.

Lebanese Muslim Association secretary Gamel Kheir said the manifesto had created a sense of vulnerability and insecurity for members of the Muslim community in going anywhere in public.

"When places of worship of any kind, or other places like community halls, when they're targeted, it does strike fear," he told AAP.

He said Brookes had a lot to answer for, wanting maximum impact by targeting Sydney's largest, oldest mosque.

"To write a whole manifesto shows just the level of depravity and hatred that someone has for a community collectively," he said.

Brookes has pleaded guilty to three counts of sending a document threatening to kill.

He has yet to enter a plea to a fourth charge relating to a separate letter sent to NSW Labor MP Jason Clare in late 2023. That document called for hatred against the Jewish community, court documents seen by AAP allege.

Brookes appeared by video link wearing a prison-issued green top from Silverwater prison during a brief hearing at Bankstown Local Court on Tuesday.

Magistrate George Breton postponed the man's sentence hearing to April 14 to get clarity on the charges, particularly the contents of the letter sent to Mr Clare.

The manifesto referred to Senator Lidia Thorpe, the mass shooting at a Hanukkah celebration at Bondi Beach, two nurses who allegedly threatened to kill Israeli patients, and pro-Palestinian protests held on the anniversary of the October 7 attacks by Hamas.

Brookes called for mass deportations, a ban on immigration, and a total ban on protests.

The manifesto ended with a dive into numerology and how January 26 / 'Australia Day' in 2026 showed "rebirth," "regeneration" and "new beginnings".

Brookes' fingerprints were found on the letters he sent out, court documents say.

Police raided his Belmore home two days on January 24, two days before Invasion Day.

He was arrested, charged and placed into custody before bail was refused.

AAP