Handwritten scraps of paper bearing the email address [email protected] were found in a bin at the family home of Salman and Hashem Abedi in the aftermath of the attack on May 22 2017, which killed 22 and injured hundreds of others, the Old Bailey was told.
Among those killed were Sorrell Leczkowski, 14, from Adel, Leeds; Courtney Boyle, 19, a Leeds Beckett University student from Gateshead; Kelly Brewster, 32, from Sheffield; Wendy Fawell, 50, from Otley; and Angelika and Marcin Klis, a couple from York.
Hashem, the younger brother, is accused of plotting with 22-year-old Salman, who died in the suicide bombing as concert-goers left the Ariana Grande gig.
The brothers allegedly duped friends and associates into helping to buy components of the explosive TATP, while switching vehicles and phones to ensure their actions went undetected.
They also found an unused address near their home to take delivery of the chemicals ordered on Amazon using others' bank details and fake emails, it was alleged.
On Thursday, prosecutor Duncan Penny QC said the bedab7 email address was created on March 20 2017 while connected to free wifi in the Hulme Market area of south Manchester.
Automatic number plate recognition (ANPR) data placed a Toyota Aygo bought by Hashem at the scene, it was alleged.
The vehicle, bought for £250, was later wrecked in a road crash, allegedly scuppering the brothers' plans to transport chemicals to a home they were renting in Rusholme, south Manchester.
That address - 44 Lindum Street - was used to order delivery of 30 litres of hydrogen peroxide, one of TATP's three components.
The bedab7 email was used to make the purchase, the court was told.
Mr Penny said: "After the explosion, the same email address was found on handwritten torn-up pieces of paper in one of the bins at the Elsmore Road address.
"Translated, 'bedabjeana' means 'To slaughter we have come', or 'We have come to slaughter'."
The court heard that police stopped Mohammed Younis Soliman, Hashem's friend, at Manchester Airport the previous month.
They seized his phone and downloaded data, which linked the purchase of 10 litres of sulphuric acid, Mr Soliman and the Abedis, jurors heard.
However, the connection was only made when the data was analysed after the blast.
Mr Penny said acquiring large quantities of chemicals risked raising "awkward questions in even the most gullible people".
The prosecutor said the Abedis therefore began using the Rusholme property in March to take receipt of Amazon deliveries.
However, their plans were temporarily thwarted when the Toyota allegedly used to transport chemicals crashed, forcing them to abandon it and run away.
Mr Penny told jurors how witnesses noticed there were some plain cardboard boxes in the Toyota's back seat, and that the car's occupants tried to remove those labels when it was discovered the Aygo could not be repaired.
Mr Penny said: "At the time, to those concerned, this may have seemed like just another road traffic collision involving an uninsured vehicle with little chance of locating the driver."
A third car, a Nissan Micra, was also in the brothers' possession for just over 24 hours on April 13/14, the court heard.
After the bombing the Micra was found parked up in the Rusholme area of Manchester, the court heard.
Inside, police found Hashem's fingerprints, some bags of screws and nails handled by the defendant and more than 10 litres of sulphuric acid in the boot and traces of TATP, the court was told.
Jurors were told how both Abedi brothers had visited a B&Q store in Stockport where their mother's card was used to buy alleged bomb-making tools, including a claw hammer, hacksaw, metal cutters and pliers at the end of March.
In April, Salman and Hashem Abedi's older brother booked them a one-way ticket to Libya with their parents, prompting them to quickly buy the Nissan on Gumtree to store the bomb-making chemicals, jurors heard.
Mr Penny said: "The entire episode smacks of real urgency."
On May 18, just four days before the bombing, Salman returned to the UK alone to finalise his plans, the court heard.
Hashem, originally from Manchester, denies the murder of 22 men, women and children aged between eight and 51.
He also denies attempted murder and conspiring with his brother to cause explosions.
The trial continues and is due to last for eight weeks.