Residents in the Highwoods area have been affected, with some telling the Gazette they have gone up to two weeks without receiving letters.
In some cases, a dozen letters have suddenly come through at once, by which time deadlines and hospital appointments have been missed.
There are fears the situation may get worse over the coming weeks as the Royal Mail approaches its busiest time of year.
Sean Hughes, 56, of Tony Webb Close, said Colchester had gained a reputation for how long residents have to wait to receive letters.
He said: “I am waiting for important documents and so is my wife – it’s worrying.
“It’s famous around the country that Colchester mail is so slow – it’s because it’s so understaffed.
“All the shareholders are milking if for as much as they can, and then they will sell it back to the Government so they can pick up the pieces.”
Tracy Farrow, 63, also of Tony Webb Close, said she had missed hospital appointments because letters had come through more than a week late.
She said: “You get things like hospital appointments which I have had a couple of, and the letters arrive after the date of the appointment, so I haven’t attended.
“That has happened a couple of times – I have had it the same day as the appointment and I have had it when the letter comes around a couple of days later.”
Patrina Boast, 68, of Sioux Close, said postal delays have made it difficult for settle her late husband’s affairs.
But a spokesman for the Royal Mail said deliveries to the area are continuing as normal and that staffing levels are close to capacity.
He said: “We can confirm deliveries to the area are continuing as normal.
“Items that enter the delivery office are being delivered according to their time frames.
“If there is a delay we will prioritise the customer’s route and ensure their item is delivered the following day.
“We are also well prepared for Christmas with staffing levels close to full and agency workers being brought in to counteract incidences of sick absence.
“We would encourage anyone who has concerns about their deliveries to contact us directly.”