The incident happened at around 11.20pm on Wednesday, March 20, when a 59-year-old woman was passing the rear of the Royal Mail sorting office in Mill Hill Lane, Musselburgh.
A man approached from behind, pushed her onto the ground and pulled her handbag from her shoulder. He then left the scene in an unknown direction.
The woman had a minor head injury and was taken to the Edinburgh Royal Infirmary as a precaution.
Police were contacted and officers are now appealing for witnesses.
The suspect is described as white, slim, in his 20s and around 5ft 7in. He was wearing a black baseball cap and a light grey bomber jacket.
Detective Inspector Ben Leathes, of the Lothians and Scottish Borders Criminal Investigation Department, said: “This was a violent and unprovoked attacked, which left the victim injured.
“We are eager to trace the man responsible and wish to speak to anyone who was in the Mill Hill Lane area of Musselburgh on the night of Wednesday, March 20.
“I would ask anyone with information, or who recognises the description of the man, to get in touch with police as soon as possible.”
Those with information can contact Police Scotland on 101, quoting incident number 4601 of March 20, or report this anonymously via Crimestoppers on 0800 555 111.
Sign up to our newsletter: enter your email in the box at the top of this article to get daily updates straight to your inbox.