Brentwood Borough Council leader Louise McKinlay (second in from right) with residents on Oliver Road in Shenfield
The postal service has blamed "a number of vacancies" for deliveries being delayed by up to 12 days in Brentwood.
Residents from across the town and Pilgrims Hatch have complained about the reliability of mail deliveries over the past six months.
Leader of Brentwood Borough Council, Councillor Louise McKinlay revealed on Sunday (December 4) that the postal service's county manager accepted in a meeting with her that "there had been issues".
She said: "There have been a series of unfortunate and unforeseen events which resulted in a number of vacancies in delivery staff.
"The situation has been resolved for now through overtime whilst they recruit additional members of staff. Two more are due to start the week after next and another in the new year.
"They expect service to resume as normal with immediate effect. We are keeping in close contact so I will continue to monitor."
Linda Ward, who lives in Harewood Road, Pilgrims Hatch, said she had one letter dated October 28 which arrived on November 9.
"It was a tax related thing for my business, but this has been going on for months. We only get post two or three times a week, it's really annoying," said the 46-year-old.
"I wrote an article for a magazine and they posted out a pre-publication copy and it didn't come until the magazine was out in the shops."
As well as post arriving late, residents have also complained that it is often delivered to the wrong address.
Caroline Lynch, who lives on Oliver Road in Shenfield, said the problems were not the fault of the staff, but of the management of Royal Mail.
READ MORE: Essex Santa sleigh routes for Christmas 2016 in Brentwood, Billericay and Ongar
"How can they let staff get so low that they can't send mail?" she said.
"I got a knock on the door and the postman handed over loads of mail. He said 'you haven't had any mail for a while looking at this' and said they are really short staffed."
The 46-year-old said the lateness of her post was concerning because she often receives hospital letters late.
"We are ringing them up saying 'where is it?' but they have sent it, you just get it days later.
"I had breast cancer last year and I have to have regular checks with oncology. I had one on Wednesday, who knows if they will refer me for something else?"