The Royal Mail has apologised to customers across Kent and East Sussex who have been experiencing long postal delays.
The BBC has heard from people in Rochester, Sevenoaks and Canterbury in Kent, and Eastbourne and Lewes in East Sussex, complaining about important documents being delayed by up to three weeks.
Tunbridge Wells resident Martin Webster said in a letter to the BBC that postal deliveries were "appalling and getting worse", adding that he had raised the issue with the town's MP.
Royal Mail regional operations director Jay Brooks said he wanted to apologise to anyone affected by delays, adding: "I want to reassure people that the vast majority of mail does arrive to the intended recipient on time."
Responding to Mr Webster, Tunbridge Wells MP Mike Martin said he had heard similar stories from other constituents.
"So many of us rely on Royal Mail to deliver crucial letters, " Mr Martin said in a letter.
"So, it's very concerning to see standards are slipping. I am particularly concerned about the number of constituents who have gotten in touch to tell me that important NHS and business letters have gone astray.
"I note that Ofcom recently fined Royal Mail for a second year in a row for its poor performance. A new owner has just been approved to take over Royal Mail by the government, so let's hope they have a better attitude toward the running of this vital service."
However, some people wrote to the BBC praising the Royal Mail service.
Kathy said, "My postman in Hildenborough is amazing. Not only does he deliver our mail on time, he also looks out for everyone on his round checking in that we're ok. He's just brilliant."