Royal Mail has admitted its quality of service does not meet its own standards in Eastleigh and are "working to further improve deliveries".
It comes as Eastleigh MP Liz Jarvis criticised the company for consistently missing delivery targets.
In the SO postcode area, only 82.8 per cent of first-class deliveries arrived on time, falling short of the 93 per cent target.
Ms Jarvis described the current performance as "failing," saying: "These missed targets are shocking and are leaving countless people in the lurch here in Eastleigh.
"This saga has been going on for far too long and people are rightly sick to the back teeth of it."
In response, a Royal Mail spokesperson said: "We acknowledge that our quality of service is not yet where we want it to be, and we’re working hard to deliver the standard our customers in Eastleigh expect."
They added that letter volumes have declined significantly in recent years, meaning many households no longer receive post every day.