The delivery and routing of messages by the Internet Message Transfer Agent (IMTA) is based on the user and group (distribution list) entries stored in the directory service. The IMTA needs to access the directory information for each message that it processes. Rather than querying the directory service each time it processes a message, the IMTA caches the directory information, or takes a snapshot of the directory information and stores it, and accesses directory information in the cache. The IMTA implements the cache for the following reasons:
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Performance - Performing a directory query for each recipient of each message is time-consuming and puts a large load on the mail server. |
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Data formatting - The information stored in the directory service is not always in the format needed by the IMTA. When creating the cache, the IMTA reformats the directory information. |
The directory information stored in the directory service is continuously updated. As a result, the directory information in the IMTA-directory cache must be updated periodically with the current directory information in the directory service or synchronized. Two types of synchronization exist:
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Full synchronization - The existing cache is replaced with a new cache, completely rebuilt with the current user and group entries from the directory service. After the synchronization occurs, the IMTA configuration file is rebuilt then the IMTA is automatically restarted. |
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Incremental synchronization - The existing cache is updated with user and group entries that were created or modified since the last full or incremental synchronization. The IMTA is not restarted. |
TABLE 1-1 outlines the updates to the IMTA-directory cache that are and are not performed during a full synchronization and an incremental synchronization.
TABLE 1-1 Updates Performed During Full/Incremental Synchronizations
For more information on user and group entry attributes, refer to "User Entries" on page 29. For more information on distribution lists, refer to "Distribution Lists" on page 18.
By default, the Internet Message Transfer Agent (IMTA)-directory cache is fully synchronized every day at 2:00 am and incrementally synchronized every hour.
The Administration Console enables you to reconfigure the synchronization schedule. Before reconfiguring this schedule, you must consider the following:
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A full synchronization requires that the IMTA be restarted, an operation that is performed automatically. Since restarting the IMTA is a CPU-intensive operation and will temporarily affect the overall mail server performance, Sun recommends scheduling full synchronizations at times when you anticipate that the mail server load is light, for example, during lunch hour or in the middle of the night. |
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An incremental synchronization does not burden the CPU to the degree that a full synchronization does; in fact, the more often incremental synchronizations are performed, the less it burdens the CPU. However, an incremental synchronization does use CPU cycles and you do not want to schedule this operation more than necessary. |
Depending on the number of users (mailboxes) your mail server services, scheduling one to six full synchronizations per day and incremental synchronizations every 5 to 30 minutes is sufficient.
Note - You must schedule directory caches on each mail server to be fully or incrementally resynchronized at the same time. Not doing so could cause routing loops to occur.
For information on reconfiguring the synchronization schedule using the Administration Console, refer to "Alias Synchronization Schedule" on page 104.