A post-marked stamp from the Ultimo Post Office, c. 1934.
The Powerhouse Museum has a number of post-marked stamps in its collection, from the Ultimo Post Office, dating between 1934-1972. The old Post Office building in Ultimo is on the corner of Harris St and Macarthur (now owned by the Powerhouse). See the catalogue record here.
With the recent closure of the Glebe Post Office - we still have Pyrmont Post Office left, and one at Broadway.