These entries show that a message from jack@vstout.vbrew.com to jill@vbrew.com was successfully delivered to a mailbox on the local host. Message arrivals are flagged with <=, and deliveries with =>. There are two kinds of delivery errors: permanent and temporary. A permanent delivery error is recorded in a log entry like this, flagged with “**”: 2000-01-30 14:48:28 12EvcH-0003rC-00 ** bill@lager.vbrew.com R=lookuphost T=smtp: SMTP error from remote mailer after RCPT TO: : host lager.vbrew.com [192.168.157.2]: 550 … User unknown After a failure like this, Exim sends a delivery failure report, often called a bounce message back to the sender. Temporary errors are flagged with “==”: 2000-01-30 12:50:50 12E9Un-0004Wq-00 == jim@bitter.vbrew.com T=smtp defer (145): Connection timed out This error is typical for a situation in which Exim properly recognizes that the message should be delivered to a remote host, but is not able to connect to the SMTP service on that host. The host may be down or there could be a network problem. Whenever a message is deferred like this, it remains on Exim’s queue and is retried at intervals. However, if it fails to be delivered for a sufficiently long time (usually several days), a permanent error occurs and the message is bounced. If you are unable to locate your problem from the error message Exim generates, you may want to turn on debugging messages. You can do this using the -d flag, optionally followed by a number specifying the level of verbosity (a value of 9 gives maximum information). Exim then displays a report of its operation on the screen, which may give you more hints about what is going wrong. Compiling Exim Exim is still under active development; the version of Exim included in Linux distributions is probably not the latest release. If you need a feature or a bugfix found in a later release, you have to obtain a copy of the source code and compile it yourself. The latest release can be found via Exim’s web page at http://www.exim.org/. Linux is one of the many operating systems supported by the Exim source. To compile Exim for Linux, you should edit the src/EDITME file and put the result in a file called Local/Makefile. There are comments in src/EDITME that tell you what the various settings are used for. Then run make. See the Exim manual for detailed information on building Exim from source. Mail Delivery Modes As noted previously, Exim is able to deliver messages immediately or queue them for later processing. All incoming mail is stored in the input directory below /var/spool/exim. When queueing is not in operation, a delivery process is started for each message as soon as it arrives. Otherwise, it is left on the queue until a queue-runner process picks it up. Queueing can be made unconditional by setting queue_only in the configuration file, or it can be conditional on the 1-minute system load by a setting such as: queue_only_load = 4 which causes messages to be queued if the system load exceeds 4.117 If your host is not permanently connected to the Internet, you may want to turn on queueing for remote addresses, while allowing Exim to perform local deliveries immediately. You can do this by setting: queue_remote_domains = * in the configuration file. If you turn on any form of queuing, you have to make sure the queues are checked regularly, probably every 10 or 15 minutes. Even without any explicit queueing options, the queues need to be checked for messages that have been deferred because of temporary delivery failures. If you run Exim in daemon mode, you must add the The system load is a standard Unix measure of the average number of processes that are queued up, waiting to run. The uptime shows load averages taken over the previous 1, 5, and 15 minutes.
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