The term circular letter is questionable. So called circular letter is actually announcement letter which is a very right term.
MOHAMMED ALI JINNAH ROAD, KARACHI
March 1, 20___
M.A Jinnah Road
Subject: Shifting to new location
We are please to inform you that the offices of our company have shifted from Salma Center,Jinnah Road to the following new location.
Abdullah Haroon Road,Karachi
Now the purchasing, marketing, accounting, and stores department will be at Ist, 2nd, 3rd and 4th floor respectively.
The shift had become necessary due to our rapidly growing business. Our clients will now enjoy more convenience and attention.
We are always pursuing to discover new ways to serve you better.