The $R metacharacter provides an appropriate filter for the URL. The intent is to produce a filter that searches all the attributes that might contain an email address for a particular user or group. The list of attributes to search comes from the configutil parameter local.imta.mailaliases. If this parameter is not set, the local.imta.schematag configutil parameter is examined, and depending on its value, an appropriate set of default attributes is chosen as follows:
The value of local.imta.schematag can be a comma-separated list. If more than one schema is supported, the combined list of attributes with duplicates eliminated is used. The LDAP_SCHEMATAG MTA option can be used to override the setting of local.imta.schematag specifically for the MTA.
Additionally, the filter searches not only for the address that was originally supplied, but also for an address with the same local part but the domain that was actually found in the domain tree, which was saved in the second step in the section entitled 188.8.131.52 The $V Metacharacter. The iterative nature of the domain tree lookup means the two addresses may be different. This additional check is controlled by bit 1 (value = 2) of the DOMAIN_UPLEVEL MTA option in the option.dat file. Setting the bit enables the additional address check. The default value of DOMAIN_UPLEVEL is 0.
For example, suppose that the domain siroe.com appears in the domain tree. Assuming Sun LDAP Schema 1 is in force, a lookup of the address
The filter that results from the expansion of $R and an ims50 schematag looks like:
(|(firstname.lastname@example.org) (email@example.com) (mailAlternateAddressfirstname.lastname@example.org) (mailAlternateAddressemail@example.com) (mailEquivalentAddressfirstname.lastname@example.org) (mailEquivalentAddressemail@example.com))
If, on the other hand, DOMAIN_UPLEVEL was set to 1 rather than 3, the filter would be:
(|(firstname.lastname@example.org) (mailAlternateAddressemail@example.com) (mailEquivalentAddressfirstname.lastname@example.org))