The job of the mailhub is to receive incoming mail from the outgoingmailers via the MX record mailhub.mit.edu and deliver to the next hop mailer. The next hop mailer is either a local post office server or the dmz mailer via its MX record (for all other MIT and non-MIT destinations). This sorting is currently performed by looking at he .LOCAL extension of the alias. The mailhub neither accepts mail from or delivers mail directly to end-user systems.
The mailhub contains a full alias database fed from moira (service:nmailhub) and updated on a nightly basis.
The mailhub performs a series of single thread deliveries to limit the pounding on the next hop mailers. Queued mail is a symptom of (a) dns lookup errors, (b) limits on the number of threads that exist, or (c) unresponsiveness of the next hop mailer. The tuneable paramater is the number of threads.
| /usr/local/sendmail | contains the entire sendmail hierarchy including binaries, configuration files and links to the log and queue directories (traditional locatons such as /usr/lib/sendmail and /etc/sendmail.cf are linked here) |
| /var/log/mailer | the log file for sendmail |
| /var/spool/mqueue | the mailer queue on a dedicated partition |
| /var/spool/mstatus? | the host status directories that manage the single thread deliveries |
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sched init pageout fsflush | basic Solaris system processes |
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ttymon sac | provides console login |
| vold | manages the floppy and cdrom devices |
| snmpdx dmispd mibiisa | provides network management via snmp |
| nscd | cacheing deamon for local databases |
| utmpd | manages the utmp files |
| inetd | provides basic monitoring services and kerberos remote services |
| xntpd | provides time synchronization listening to NTP broadcasts |
| named | provides name resolution (critical for sendmail) |
| cron | rolls the log files, cordinates basic cleanup services and restarts sendmail periodically |
| zhm | athena addition - provides zephyr communication services |
| update_server | athena addition - receivs updates via the moira database |
| sendmail | the mailer |