"Real" post - the Royal Mail
The main Post Office in Cambridge is on St Andrew's Street and there are a host of smaller Post Offices, at any of which you can buy stamps or send letters or parcels to anywhere in the world.
All graduate students can have post delivered to their college, and it may be preferable to use this address rather than your residential address. At most colleges, post will be placed in your pigeonhole in the Porters' Lodge. The mailing address should usually be written:
You may also be able to receive post in your department - ask where things addressed to you will be placed.
University Messenger Service (UMS)
The UMS is an internal mail collection and delivery service to University department and colleges. Your department and College will have a collection point, usually reception and the porters' lodge respectively; there's also a UMS tray in the Graduate Union offices so you can communicate with us this way. It's supposed to be used for University business and academic matters only; circulars are not allowed. As much of the mail is delivered by bike it is also best to avoid using the UMS for bulky items.
CUSU Mail Service (CUSU-MS)
CUSU also run a mail service (known as CUSU-MS, or occasionally by its previous name of "ICMS"), which delivers to colleges, but not departments, during term time only. Mass-mailings for societies and posters can be sent by this service. Again, there's a collection tray in most college Porters' Lodges.