Stamps/postage charges are exempt. This will normally arise where a department is recharging franking machine costs to a member of staff or an external body.
However, if you make a charge for postage which is connected with a supply of goods or services (e.g. posting a report as part of a consultancy service) then the postage charge will have the same liability as the goods or services provided.
Courier charges are VATable, unless the item is going outside the EC in which case they would be zero-rated.