Paul Scott, who lives in Brondesbury Road, Kilburn, was shocked to find a bundle of 35 letters held together with an elastic band dumped in his bin on June 20.
Among the letters were NHS correspondence and utility bills addressed to his neighbours.
The envelopes all bore the name Whistl, an intermediary group that sends post to the Royal Mail for delivery.
The following day, Mr Scott called the Kilburn delivery office. But after waiting 15 minutes before being given a reference number, he says he has heard nothing since.
He said: “That was Friday June 21 and now it is July 2 and those poor people are still waiting for their post.
“It’s all utility bills and brown envelopes and NHS – who knows, it’s test results or appointments, it’s all important stuff.”
The computer consultant pointed the finger at agency staff, explaining: “All the posties around here are very good and most have been doing it for years and years. But when they go on leave agency staff are brought in.
“Agency staff can’t always be bothered to do the job, find out all the different addresses, so they just dumped it.”
Mr Scott has now decided to deliver the letters himself.
He said: “I could have done it earlier but I wanted to do everything by the book. It’s an absolute scandal.
“I’m sick of these things happening. There are a lot of people making a lot of money at the top and meanwhile the service is deteriorating.”
A Royal Mail spokesperson said: “We are investigating this case as a matter of urgency.
“Our policy, which we regularly reinforce to our delivery colleagues, is to deliver all parcels and letters to customers’ addresses, or to a neighbour.
“We will be in touch with Mr Scott to discuss the matter further.”