18.8 Handling Large Numbers of Access Entries

Sites that use very large numbers of entries in mapping tables should consider organizing their mapping tables to have a few general wildcarded entries that call out to the general text database for the specific lookups. It is much more efficient to have a few mapping table entries calling out to the general text database for specific lookups than to have huge numbers of entries directly in the mapping table.

One case in particular is that some sites like to have per user controls on who can send and receive Internet email. Such controls are conveniently implemented using an access mapping table such as ORIG_SEND_ACCESS. For such uses, efficiency and performance can be greatly improved by storing the bulk of the specific information (e.g., specific addresses) in the general text database with mapping table entries structured to call out appropriately to the general text database.

For example, consider the ORIG_SEND_ACCESS mapping table shown below.

ORIG_SEND_ACCESS
 
! Users allowed to send to Internet
!
  *|adam@siroe.com|tcp_local|*    $Y
  *|betty@siroe.com|tcp_local|*   $Y
! ...etc...
!
! Users not allowed to send to Internet
!
  *|norman@siroe.com|tcp_local|*  $NInternet$ access$ not$ permitted
  *|opal@siroe.com|tcp_local|*    $NInternet$ access$ not$ permitted
! ...etc...
!
! Users allowed to receive from the Internet
!
  tcp_*|*|*|adam@siroe.com        $Y
  tcp_*|*|*|betty@siroe.com       $Y
! ...etc...
!
! Users not allowed to receive from the Internet
!
  tcp_*|*|*|norman@siroe.com      $NInternet$ e-mail$ not$ accepted
  tcp_*|*|*|opal@siroe.com        $NInternet$ e-mail$ not$ accepted
! ...etc...
      

Rather than using such a mapping table with each user individually entered into the table, a more efficient setup (much more efficient if hundreds or thousands of user entries are involved) is shown in the example below, which shows sample source text file for a general database and a sample ORIG_SEND_ACCESS mapping table. See 10.9.1 MTA Text Databases for set up information.

DATABASE ENTRIES

SEND|adam@domain.com    $Y
SEND|betty@domain.com   $Y
! ...etc...
SEND|norman@domain.com  $NInternet$ access$ not$ permitted
SEND|opal@domain.com    $NInternet$ access$ not$ permitted
! ...etc...
RECV|adam@domain.com    $Y
RECV|betty@domain.com   $Y
! ...etc...
RECV|norman@domain.com  $NInternet$ e-mail$ not$ accepted
RECV|opal@domain.com    $NInternet$ e-mail$ not$ accepted


MAPPING TABLE

ORIG_SEND_ACCESS

! Check if may send to Internet
!
  *|*|*|tcp_local       $C${SEND|$1}$E
!
! Check if may receive from Internet
!
  tcp_*|*|*|*           $C${RECV|$3}$E
      

In this example, the use of the arbitrary strings SEND| and RECV| in the general database left-hand sides (and hence in the general database probes generated by the mapping table) provides a way to distinguish between the two sorts of probes being made. The wrapping of the general text database probes with the $C and $E flags, as shown, is typical of mapping table callouts to the general text database.

The above example showed a case of simple mapping table probes getting checked against general text database entries. Mapping tables with much more complex probes can also benefit from use of the general text database.