There might be unusual cases where the mapping from domain to base DN is done some other way. In order to accommodate such setups, the URL resolution process has the ability to call an MTA mapping. This is done with a metacharacter sequence of the general form:
The double quotation (“) initiates and terminates the callout. The character immediately following the $ is the separator between the mapping name and argument; a character should be chosen that does not collide with the expected character values used in either the mapping name or argument.