623Chapter 24Running a Mail ServerInstalling and Running (Michigan web site) sendmailSendmail
623Chapter 24Running a Mail ServerInstalling and Running sendmailSendmail (http://www.sendmail.org/) is the granddaddy of SMTP mail systems. It is still the default MTA on most systems, and a recent survey showed that 41% ofactive mail servers were running sendmail. A fairly recent addition to sendmail is the Milter API. This API allows for the writingof mail filters that can filter messages at the SMTP level, allowing for careful controlover what messages are accepted by the server. A standard milter consists of a daemon that runs in the background and waits for aconnection from the sendmail daemon. Almost every line that is sent from an SMTPclient to the server is passed to the milter, which can accept, temporarily reject, orpermanently reject the message at any point in the process. Milters also have thecapability to modify message content. This capability is most commonly used toadd headers to messages indicating status information. A number of milters have been written to perform various tasks. Two such miltersare Spamass-Milter (http://savannah.nongnu.org/projects/spamass-milt/) and ClamAV-Milter (http://clamav.net/). As you would expect, these milters useSpamAssassin and ClamAV to perform content identification. You can find general information about milters at http://milter.org/. The final component is Qpopper (http://qpopper.sourceforge.net), which isthe most widely used POP3 daemon. You can find configuration options for Qpopperin /etc/qpopper.conf, although you won t need to change any of the defaults forthis server. Follow these steps to install and configure the needed software: 1.Use APT to install the sendmail packages: # apt-get install sendmail sendmail-bin sendmail-docAPT will download the packages, remove Exim (the default MTA on Debiansystems), and install sendmail. During the configuration process, you will seewarnings about databases not existing. It is safe to ignore these warnings. 2.Configure SpamAssassin s startup parameters. Start by editing the file/etc/default/spamassassinand changing the ENABLEDand OPTIONSparameters. The file should look something like this when you are done: # /etc/default/spamd.conf# Change to one to enable spamdENABLED=1# Options# See man spamd for possible options. The -d option is# automatically added. OPTIONS= -m 25 -H Note33_
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