They surpassed the previous record of 263-5, set by Royal Challengers Bangalore in 2013
He put up a ruthless batting display for Barisal Division and South Zone this year.
In his last eight innings, the right-handed batsman cracked six centuries that included three double tons with a best of 282 against Chittagong in February.
The A team called up the 19-year-old for their tour to South Africa and Zimbabwe later this month.
"I have something in mind for this tour, which is to at least be the best performer in the team," Mosaddek said after training at the Sher-e-Bangla National Cricket Stadium on Sunday.
He is keen to carry his domestic form into the A team.