The system administrator can configure Exim so that users can set up variants on their email addresses and handle them separately. Consult your system administrator or local documentation to see if this facility is enabled on your system, and if so, what the details are.
The facility involves the use of a prefix or a suffix on an email address. For example, all mail addressed to lg103-<something> would be the property of user lg103, who could determine how it was to be handled, depending on the value of <something>.
There are two possible ways in which this can be set up. The first possibility is the use of multiple .forward files. In this case, mail to lg103-foo, for example, is handled by looking for a file called .forward-foo in lg103's home directory. If such a file does not exist, delivery fails and the message is returned to its sender.
The alternative approach is to pass all messages through a single .forward file, which must be a filter file in order to distinguish between the different cases by referencing the variables $local_part_prefix or $local_part_suffix, as in the final example in section 33 below. If the filter file does not handle a prefixed or suffixed address, delivery fails and the message is returned to its sender.
It is possible to configure Exim to support both schemes at once. In this case, a specific .forward-foo file is first sought; if it is not found, the basic .forward file is used.
The personal test (see section 28) includes prefixes and suffixes in its checking.