pending Messages enterpending state when they arrive, and remain there until they are marked as spam or nonspam. These messages are displayed in the Web-based “Pending Messages” list.
spam The spam-control officer can mark a message as spam. If a message marked asspamis re- ceived, a rejection notice is sent to the sending mail server, and the message is not delivered.
not-spam The spam-control officer can mark a message asnot-spam. If a message marked asnot- spamis received, it is delivered as usual.
2.7
Handling of Suspect Messages
As discussed earlier, CanIt-Domain-PRO may be configured to issue an SMTP temporary failure response if a message is held because it is suspected of being spam. This response ensures that the message remains in the sender’s queue. The sender will retry transmission periodically, until one of three things happens:
• The message is marked asspam. On the next transmission attempt, it will be rejected with a permanent failure response.
• The message is marked asnot-spam. On the next transmission attempt, it will be accepted and delivered.
• The sending relay times out and bounces the message. Most relays retry transmissions for at least 3 days, so this will not happen unless you do not check the spam quarantine often enough.
2.7.1 Handling Methods
While keeping the message in the sender’s queue is useful, it does mean that your CanIt-Domain-PRO installation relies on the server to retransmit. It also may consume excessive bandwidth on a busy site. Therefore, CanIt-Domain-PRO has three options for handling suspicious messages:
1. The default handling,Until-Dispatched, always replies with a temporary failure indication until the CanIt-Domain-PRO operator marks a message asspamornot-spam.
2. TheFirst-Timehandling replies with a temporary failure indication thefirsttime a suspicious message is received. A lot of spamming software ignores error returns and will never retransmit the message. Failing it the first time, therefore, stops a lot of spam without human intervention. If the message is transmitted a second time, however, it is accepted and held in the CanIt- Domain-PRO database. If the operator marks the messagespam, it is simply deleted from the database. If the message is markednot-spam, CanIt-Domain-PRO re-mails it to the original recipient before deleting it from the database.
3. TheNeverhandling never replies with a temporary failure indication. Suspicious messages are always accepted and then held in CanIt-Domain-PRO’s database. Incoming messages immedi- ately move to thependingstate.
Please note that holding messages locally may greatly increase the disk space used by CanIt-Domain- PRO. Be sure to leave enough disk space to handle all messages you anticipate will be held locally.
2.7.2 Secondary MX Relays
Many organizations have secondary MX hosts that queue mail if the primary host is down. They then relay the queued mail when the primary MX host comes back up. Ideally, CanIt-Domain-PRO should run on all of your MX hosts. However, if it can only run on your primary MX host, then all other MX hosts should relay to the CanIt-Domain-PRO machine. You should then tell CanIt-Domain-PRO the IP addresses of the secondary MX hosts via the “Known Networks” facility so that CanIt-Domain-PRO can use theNever Tempfailhandling for messages from thoses hosts. (There is no point in keeping mail queued and retransmitted on your secondary MX hosts; it’s better to accept and hold the message on the CanIt-Domain-PRO machine.)
2.8
The Database
The incident database is key to the correct operation of CanIt-Domain-PRO. Three different agents operate on the database as shown in Figure2.5:
Incidents Database Web−Based
GUI Periodic Jobs
CanIt Filter
Figure 2.5: Database Agents
The agents operating on the database are:
• The CanIt-Domain-PRO Filter – This is the portion of CanIt-Domain-PRO that integrates with Sendmail and disposes of spam messages.
• The Web-Based GUI – This is used by users or administrators to mark messages as spam or legitimate. The Web-Based GUI also lets you monitor the levels of spam and take action against specific senders, domains or relay hosts.
• Periodic Jobs – These housekeeping jobs perform operations like moving expired pending mes- sages intospamstatus and purging very old messages from the database. Periodic jobs may be started from one of two places:
2.9. REMAILING MESSAGES 39
1. The/usr/share/canit/scripts/canit.cronscript, which should be run once a night.
2. As part of the operation of the CanIt-Domain-PRO daemon (canitd). Canitd is a daemon that starts on bootup and runs continuously, performing background maintenance tasks.
2.9
Remailing Messages
On occasion, CanIt-Domain-PRO will be forced to remail a message after discarding the original. The following scenarios cause remailing:
1. If a message comes in for recipients in more than one stream, CanIt-Domain-PRO generates one new copy foreachstream and mails out the copies. The original message is then discarded. You may see a message in the log file indicating that the message has been discarded; don’t panic. The copies are safely queued.
2. If a Pending message is held in the database and subsequently approved for release, CanIt- Domain-PRO fetches the message body from the database and remails it. This always takes place on the designated ticker host, no matter which host processed the original message. In all cases when CanIt-Domain-PRO remails a message, the message goes into Sendmail’s submission queue (most likely in the queue directory /var/spool/clientmqueue or /var/spool/mqueue-client. The message is only processed on the next run of the submis- sion queue. For this reason, you should keep the submission queue interval short (on the order of a minute or two.) On CanIt-Domain-PRO appliances, the submission interval is automatically config- ured for you. On other platforms, consult your system’s documentation for details on how to shorten Sendmail’s submission queue interval.
Chapter 3
Realms
3.1
Introduction to Realms
CanIt-Domain-PRO has three levels of administrative control:
1. TheSystem Administratoradministers all aspects of CanIt-Domain-PRO and is responsible for setting up and provisioning the system.
2. ARealm Administratoradministers settings and rules for a givenrealm. A realm encompasses one or more Internet domains. The realm administrator is responsible for provisioningstreams within his or her realm. A realm administrator is said to haveroot privilegeswithin a realm. 3. A Stream Owner administers settings and rules for his or her own stream. A stream owner
is typically an end-user or a person responsible for administering a small group of e-mail ad- dresses.
The administrative levels are illustrated in Figure3.1below:
Realm Administrator Realm Administrator Realm Administrator
Stream Owner Stream Owner
Stream Owner Stream Owner System Administrator
Realm 2
Realm 1 Realm N
Stream 1 Stream N
Stream 1 Stream N
Figure 3.1: Administrative Levels
3.2
Realm Names
A realm name can consists only of letters, numbers, dashes and underscores. That is, only the follow- ing characters can appear in a realm name:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 0 -
Realm names are case-sensitive; a realm namedREALM-ONEis different fromrealm-one.
3.2.1 ThebaseRealm
The realm namedbase is special. This realm always exists and cannot be deleted. Any user with root privileges in thebaserealm is considered an overall CanIt-Domain-PRO system administrator, and can access any realm and setting.
In other words, a realm administrator of thebaserealm is an overall CanIt-Domain-PRO administra- tor.