A common routine request is usually a request for information. It is routine
when the writer 1) is not asking a special favour and 2) is expecting the request to be
accepted. A typical routine letter asks for more information, catalogues, and price
quotation. The reader usually accepts the request because what is requested is usually
available at hand.
A non-routine requires individualized acknowledgement. The reader may or
may not be able to settle the request. For example, a Thai student requests a transfer
from the Heathrow Airport to a university in London. There may not be any service
to the university. The receiver may have to suggest a company which provides their
service.