A Goulburn Post reader, who asked to remain anonymous, said an important 'priority' letter, containing medical information from Bowral Hospital, did not arrive in Goulburn until nine days after the stamped postage date.

With priority postage costing an extra 50c on regular mail, the reader questioned what customers were really paying for.

The Australia Post website states priority letters are estimated to be delivered from Bowral to Goulburn within two business days, while regular post is four.

"...We consistently meet or exceed our required Community Service Obligation of delivering 94 per cent of domestic letters on time or early," a spokesperson told the Post.

"For guaranteed next day delivery, customers can purchase Express Post prepaid envelopes.

"Upon further questioning, however, they confirmed Goulburn fell outside the 'next day delivery' network, but insisted that letters purchased as express or priority services were still likely to arrive faster than regular post.

"Customers can still use Express Post for delivery to or from areas that fall outside the EP network," the spokesperson said.

"While next day delivery is not guaranteed, the item will still be processed, handled and delivered as fast as possible."

Our staff take great pride in the timely, safe and efficient delivery of mail.

"While we recognise there may be isolated incidents of delayed mail, this is rare, and we continue to always look for ways to improve our service."