Do you know what product can add a paragraph of text to every e-mail that leaves my Exchange server, for example a disclaimer or a legal notice?
This is a common question and the answer depends on what version of Exchange you are running. For both Exchange 5.5 and 2000, the easiest way to deploy would be a third party app that does it for you.
Take a look at the following products:
Otherwise, for Exchange 5.5:
Microsoft provides imsext.dll
For Exchange 2000:
You write an SMTP transport event sink
You could (and should) also read the excellent Exchange FAQ: