An Australia Post mailman "too lazy" to do his job, who was found with almost 10,000 undelivered items in his bedroom, has pleaded guilty to theft charges.

A Melbourne court heard Mark Baguio, 28, became "overawed" with his duties and could not cope with the job he once liked.

Prosecutor Kristie Eales said Baguio had failed to deliver about 9800 pieces of unaddressed, personal or "junk" mail between February, 2009, and February, 2011.

Ms Eales told Melbourne Magistrates Court that Baguio was employed as a postal delivery officer responsible for the Williamstown and Newport areas.

She said that in January, 2011, Australia Post was advised that a yellow mail delivery bag containing 755 unaddressed articles had been dumped in a rubbish bin in a West Sunshine street outside Baguio's flat.