7 CONCLUSIONES
7.3 Propuestas de mejora en las medidas establecidas para la supresión efectiva de la violencia de
Isode recommends that you use LASER configuration for Internet users, which means you should use the dns-table-laser lookup policy unless you wish to override the values configured in DNS (for example, if you are using domain synonyms).
LASER is described in Chapter 5, Managing Internet Users Using LASER Routing. The rest of this description of routing assumes you have chosen not to use LASER configuration of Internet users.
For a detailed explanation of routing see the M-Switch Advanced Administration Guide. However, in simple terms when routing an Internet email address, the first stage determines: • if the domain is valid
• if the domain is local
• if it is local, if there is a table prefix to be used later.
The process that determines whether the domain is valid and local depends on the lookup policy. There are three places where information can be held:
• DNS • Routing trees • Tables
Lookup policies use these as described in Table 4.1, “LASER lookup policies for message routing”.
You can configure lookup policies as a sequence in which each is tried until routing succeeds. For a more detailed description of routing and routing lookup policies, see the M-Switch Advanced Administration Guide.
4.6
Routing policies
The lookup policy (Section 4.3, “External MTAs”) determines where channels are to look for information on how to route messages. A default policy for all channels is set in the configuration for the MTA but you can override this for individual channels.
Channel properties can be displayed and modified from the Switch Configuration view in the same way as MTA properties and the lookup policy fields for both work in the same way.
To view the default lookup policy for an MTA, select the MTA in the Switch Configuration view and click the Lookup tab in the page on the right. The current policy is displayed in the Lookup policies field under the heading Default Routing policies for the MTA. To change it or add a value, click Edit.
To view the inbound lookup policy for a channel, select the channel under the MTA and click the Advanced tab in the page on the right. Click the Lookup policy for inbound. If
no lookup policy is displayed, the default set for the MTA is used. To change the value or add a fallback value in either of these fields, click the Edit button to the right of the field. Press the Edit button in the above cases to display the Default Lookup Policy editor shown in Figure 4.12, “Default lookup policy editor”.
The effect of the policies is described below in Table 4.1, “LASER lookup policies for message routing”. The prefix window is for use with tables, see the M-Switch Advanced Administration Guide for details.
Figure 4.12. Default lookup policy editor
When routing a message, the policies are tried in the order given until routing information is found. If none of the policies can provide the necessary routing information, the message will not be delivered to this recipient and a non-delivery notification is generated, specifying that the recipient cannot be routed.
Note: If queue is included anywhere in the list, the message will be queued and processed later if temporary name-server errors occur. If queue is the first lookup policy, all messages are queued on the housekeeper channel to be processed subsequently.
Table 4.1. LASER lookup policies for message routing
Effect Value
Verifies the domain using the DNS and if the delivery would be to the local system, the address is deemed to be local.
dns-laser
Uses the domain table as in standard table-based routing
table-laser
Uses the DNS to verify the domain, but then proceeds to use the domain table, followed by LASER Lookup
dns-table-laser
If the previous Domain Name Service or Directory lookup failed because the
nssoft
information could not be read (for example, the DSA or DNS server was down), continue with the lookup policies as if the attempt to read the information was successful but no routing information was found. This policy must be preceded by a value which includes dns or ds.
Effect Value
Queue the message. This policy can be used to speed up message submission, as
queue
described in Section 4.6.1, “Configuring fast submission”.
The nssoft policy enables processing to continue in the event of a DNS or DS read failure. Normally processing for the current message would stop in such circumstances.
Table 4.2. Other lookup policies
Effect Value
The Domain Name Service (dns) is looked up initially to attempt to normalize an RFC
dns-ds
822 domain address. Then the Directory (ds) is accessed for information on how to route the address. If the Domain Name Service lookup was successful but the Directory lookup failed to produce the necessary routing information, and the address is not local, the Domain Name Service is checked again to find out where to relay this message. Uses the domain table as in standard table-based routing
dns
Look up routing information in the Directory.
ds
Normalize the address using the Domain Name Service, then look up routing information in tables.
dns-tbl
Look up routing information in tables.
table
LASER routing is recommended for Internet messaging, but the above values can be used. See the M-Switch Advanced Administration Guide for a description of how to use these values.
4.6.1
Configuring fast submission
Message submission can be speeded up by reading the messages quickly and queuing them for processing later, when the MTA is less busy. To configure this action, make queue the first default lookup policy.
Note: Speeding up submission in this way may increase the load on the system. This forces the use of the special housekeeper channel, which is described in the ‘MTA Tailoring’ chapter of the M-Switch Advanced Administration Guide. This channel is set up automatically and does not need to be configured.
The other effect is that messages to unroutable recipients will result in a report rather than being rejected in SMTP protocol.