The Alliance assembly member (MLA) Michelle Guy met Royal Mail on Tuesday.
“I’ve been hearing from people for months now on this issue, it got particularly acute now after Christmas,” she said.
The Lagan Valley MLA added that she was “overwhelmed” with responses when she asked constituents about the scale of the issue.
She said people were not receiving “vital correspondence” such as hospital appointments and banks cards and it was “having a real impact on people’s lives”.
“Having a postal service is not a luxury, it’s an expectation that we all have and right now, it’s not working.”
Speaking after meeting Royal Mail on Tuesday, Guy said she had a “bit of disappointment” that it was not “fully acknowledge that some of the complaints that have come through perhaps haven’t been taken as seriously as we would like”.
She said she felt that going forward there is a commitment to resolve the issues.
She said she will follow up with the communications regulator Ofcom regarding the issues.