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Difference between revisions of "Email"

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===master.cf===
 
===master.cf===
 
This configuration file describes how the Postfix daemon should run and determines which ports it should be listening on for connections and how to handle those connections. The default format of this file is perfectly fine, with only two additions necessary in our setup. The first is the amavis line, which is configured for spam filtering. The second is the line beginning with 127.0.0.1. This second line accepts mail on an alternate port and delivers the mail directly, bypassing spam filtering. This is the port to which amavisd-new delivers mail. If amavisd-new delivered mail to the standard postfix port, all messages would be put into an endless loop of spam filtering.
 
This configuration file describes how the Postfix daemon should run and determines which ports it should be listening on for connections and how to handle those connections. The default format of this file is perfectly fine, with only two additions necessary in our setup. The first is the amavis line, which is configured for spam filtering. The second is the line beginning with 127.0.0.1. This second line accepts mail on an alternate port and delivers the mail directly, bypassing spam filtering. This is the port to which amavisd-new delivers mail. If amavisd-new delivered mail to the standard postfix port, all messages would be put into an endless loop of spam filtering.
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===aliases===
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This configuration file describes aliases, and is located in /etc/aliases. When an alias is defined, mail is no longer delivered to a mailbox (if there is one), and is instead forwarded to the addresses listed in the aliases file.
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To update this file, edit it, <code>scp</code> it to other mail servers, then run <code>newaliases</code> on all mail servers. Changes take effect immediately upon running <code>newaliases</code>.
  
 
==Running==
 
==Running==

Revision as of 14:10, 10 May 2016

{{#set:Page describes type=Service|Criticality=Production|Contact person=2017sdamashe}}

Machines which provide this service

{{#ask:

 Page describes type::Machine
 Service provided::Email
 |?Machine type
 |?Hardware type
 |?Contact person

}}

History

The current TJ email system is an idea originally designed by Aman Gupta (class of '04). The original system was implemented by Andrew Deason (class of '06) with the help of several staff members, including Richard Washer and Susan Beasley. A second mail system, based on Zimbra, was configured by Lee Burton. The latest mail system was designed by Brandon Vargo.

Previously, the CSL only hosted mail for the CSL itself; mail that was only accesible to people with Systems Lab accounts. Today, lab-only mail does not exist anymore, and everyone gets their email off of the same system, all with @tjhsst.edu addresses.

Overview

The current mail system consists of two primary email servers as well as a mailman server. The two primary email servers, casey and smith are named after the founders of UPS and FedEx, Jim Casey and Frederick Smith, respectively. The servers are virtually identical; only the hostname/mailname and network information is different. Each runs postfix, dovecot, and amavisd-new. The mailman server, lists, runs a standard mailman installation.

When mail is first received by the mail system, it is processed by postfix. If basic spam tests pass, the message is passed to amavisd-new for additional spam processing. If the message passes these tests, it is placed into another internal postfix queue. In general, mail will only be tagged instead of being discarded. At this point, postfix is configured to pass the message to dovecot for delivery. Both servers share a common NFS filestore. Dovecot is configured to handle locking.

Authentication/Authorization

Authentication is handled by the kerberos PAM module, similar to most other systems in the lab. Dovecot is configured to user PAM.

Instead of using the Lab's LDAP tree for user information, account information is stored locally on each server in the form of standard UNIX accounts. A mail management script, described below, synchronizes the AD user information with the local UNIX accounts. The UID for the local UNIX account is a hash of the username. This allows each server to run the mail synchronization script independently and not worry about UID conflicts on the shared NFS storage.

Postfix

At the heart of the mail system is the excellent mail server Postfix. It was chosen over alternatives for its robustness, ease of configuration, and ease of use.

Configuration

Postfix configuration is accomplished through several files in /etc/postfix/. Here we will outline their general structure. After changing most configuration files, Postfix must reload its configuartion files with the command postfix reload.

main.cf

This configuration file tends to be the longest, as it houses nearly all of the options one might be concerned with. As this file is commented, there is no need to duplicate its function here.

master.cf

This configuration file describes how the Postfix daemon should run and determines which ports it should be listening on for connections and how to handle those connections. The default format of this file is perfectly fine, with only two additions necessary in our setup. The first is the amavis line, which is configured for spam filtering. The second is the line beginning with 127.0.0.1. This second line accepts mail on an alternate port and delivers the mail directly, bypassing spam filtering. This is the port to which amavisd-new delivers mail. If amavisd-new delivered mail to the standard postfix port, all messages would be put into an endless loop of spam filtering.

aliases

This configuration file describes aliases, and is located in /etc/aliases. When an alias is defined, mail is no longer delivered to a mailbox (if there is one), and is instead forwarded to the addresses listed in the aliases file.

To update this file, edit it, scp it to other mail servers, then run newaliases on all mail servers. Changes take effect immediately upon running newaliases.

Running

Running Postfix is relatively easy, with most utility coming from postfix <command>. The following commands are recognized:

  • check

Checks the configuration files without starting or stopping Postfix. Useful to check if you've made mistakes on a production machine.

  • start

Starts the Postfix mail system.

  • stop

Stops the Postfix mail system in a nice way. Processes stop naturally.

  • abort

Stops the Postfix mail system abruptly. This one should be avoided if possible.

  • flush

Flushes the mail queue, forcing Postfix to try delivering all mail that has accumulated in the queue.

  • reload

Causes Postfix to reload its configuration files and restart processes nicely.

Typically the daemon is started and stopped with /etc/init.d/postfix start and /etc/init.d/postfix stop.

Other commands of interest include mailq, which lists all mail currently stored in the queue. This can be flushed using postfix flush, as indicated above.

Postfix sends all its logging information to syslog, which usually appends it to the file /var/log/mail.log. Examining this file is often key to troubleshooting issues with the mail system.

Amavis

Amavisd-new is used to scan all incoming and outgoing mail for virii and spam. It serves as an interface between the MTA, Postfix, and the various scanning utilities: Clam Antivirus for virus protection, and SpamAssassin for spam detection.

Clam Antivirus

The ClamAV package is being used to scan for virii in email. It functions in two modes: first as a daemon that runs all the time and scans data fed to a socket, and also as a standalone command line utility, clamscan. In most circumstances we will be using the former due to its increased performance, falling to the latter only if the daemon fails.

The virus definitions are updated about five times a day off the Internet through the freshclam daemon. In this way, new virii in the wild will be detected early and stopped from entering the TJHSST mail system.

SpamAssassin

SpamAssassin is used to scan all mail coming into the lab for its likelihood of spam, and all messages are given points for certain key phrases that are common in spam. With our configuration, very little user-level configuration is available. Additional rule files have been added under /etc/spamassassin/. SpamAssassin can be run as a daemon, but the mail system is configured to use the spamassassin tool directly.

Configuration

Configuration of Amavis is relatively simple and commented well, thus its configuration file will not be repeated here. Virtually all configuration is found in the files in /etc/amavis/conf.d/. Files are processed in order.

Running

Very little needs to be done to Amavis to get it running besides making sure that all necessary daemons are running, specifically clamd, freshclam, and amavisd-new. When Amavis receives a new mail on its socket, it will pass it through the virus scanner and then either discard the email or approve it and add an email header that indicates it was passed. It will then run the email through SpamAssassin and add any necessary headers indicating spam level. No spam will automatically be discarded; it is up to the user to filter as s/he wishes. Dovecot will automatically put spam in a spam folder.

Logging information is sent to syslog, which typically appends it to /var/log/mail.log. In this will be indicated whether the emails passed or were infected, and in the case of the latter, which virus/ii were involved.

Mailman

E-mail distribution lists are provided on the domain lists.tjhsst.edu by Mailman, a highly popular software package. Most list administration takes place through an easy online interface at https://lists.tjhsst.edu/, though many functions are also available through email, such as list subscription and some message handling.

Configuration

Configuration for this software package is minimal; the main parameters that must be specified are the urls and domains to be used. A modified version of the main postfix+amavisd-new configuration files are used. Integration with Postfix is achieved through the postfix-to-mailman.py script, which provides the necessary functionality.

Running

Postfix pipes any email with a destination of lists.tjhsst.edu to this script, which runs the necessary Mailman commands to deliver the email. Mailman, of course, ends up sending mails back to Postfix, destined for the actual recipients. Postfix will then deliver these mails to the mail mail systems or forward them to the appropriate mail server.

A few daemons must be running for Mailman to function properly. The first is qrunner, which processes any mail in Mailman's queue. If this is not running, e-mails to lists will be added to the queue but will never be delivered to recipients. This is started by the mailman init script. The other necessary daemon is apache, which provides the necessary online interface for list administration.

Dovecot

Dovecot proves IMAPs, POPs, and sieve support, in addition to being the local mail delivery agent. Dovecot receives mail from postfix and is responsible for delivering it to the user's mail directory. If dovecot is not running, postfix will queue mail.

Dovecot also supports quotas. If a user is over their soft quota, dovecot will give a warning but still store the message. If a user exceeds their hard quota, the mail message will be rejected.

Account Management

See Account provisioning for information on running the synchronization script.

The mail.py script is a python script responsible for syncing the local user information with the Active Directory user database. This script should be run on all mail servers, even though there is a common file storage.

Users are stored in groups in AD according to whether a mail account is required and the desired quota. This information is compared to a local user database, /etc/mailmanage/users, a CSV file that lists all mail users past and present. Users in AD that are not in the local database will have accounts created. Users in the local database but not in AD will have their account disabled unless an override is specified. Currently it is necessary to edit this file directly to override a quota or keep an account enabled.

CSV fields:

  1. The username
  2. The quota, before the multiplication value is taken into effect
  3. Source of the user account
    • There are two values: ldap and override. A ldap source means the user comes from ldap and user attributes should be overridden on sync. A type of override means the local values should not be replace by those in AD. This is useful for overriding quotas or keeping accounts enabled that would otherwise be disabled.
  4. Enabled/disabled state

The script is commented, so its internal workings will not be copied here. However, of particular note is the perform_actions variable at the top of the parameters section of the script. This variable should be set to 0 for an initial test run, in order to perform a sanity check of the output. The script will print all actions it will perform, including exact commands that it will run. Setting this variable to 1 will result in the script actually running these commands.

Storage

Mailboxes are stored on the Sun StorEdge D2 array Skillet which also houses the main AFS volumes. The mail servers are configured to mount the NFS share from nfs-mail.tjhsst.edu, which is primarily hosted on Dulles. This hostname is controlled by Solaris Cluster, and will automatically fail over to Seatac should the primary host fail.