191 lines
6.6 KiB
Plaintext
191 lines
6.6 KiB
Plaintext
E-MailRelay Reference Manual
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============================
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Document
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--------
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This is the E-MailRelay reference guide. It contains material which is supplementary
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to the user guide.
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Usage
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-----
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The "emailrelay" program supports the following command-line usage:
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emailrelay [<switch> [<switch> ...]]
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where <switch> is:
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* --version (-V)
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Displays version information and exits.
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* --admin (-a)
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Enables the administration interface and specifies its listening port number.
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* --as-server (-d)
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Equivalent to "--close-stderr --log".
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* --close-stderr (-e)
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Closes the standard error stream when daemonising.
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* --forward (-f)
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Forwards stored mail on startup (requires --forward-to).
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* --help (-h)
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Displays help text and exits.
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* --pid-file (-i)
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Records the daemon process-id in the given file.
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* --log (-l)
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Writes log information on standard error (if open) and syslog (if not disabled).
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* --no-syslog (-n)
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Disables syslog output.
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* --forward-to (-o)
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Specifies the remote smtp server (required by --forward and --admin).
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* --port (-p)
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Specifies the smtp listening port number.
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* --as-client (-q)
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Equivalent to "--no-syslog --no-daemon --log --dont-serve --forward --forward-to".
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* --remote-clients (-r)
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Allows remote clients to connect.
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* --spool-dir (-s)
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Specifies the spool directory (default is "/usr/local/var/spool/emailrelay").
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* --no-daemon (-t)
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Does not detach from the terminal.
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* --verbose (-v)
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Generates more verbose logging (if compiled-in and logging enabled and stderr open).
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* --dont-serve (-x)
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Stops the process acting as a server (usually used with --forward).
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If no command-line switches are supplied at all then the default
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behaviour is:
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* to run as a daemon, detached from the terminal
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* listen on the standard SMTP port (25)
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* store e-mail messages in "/usr/local/var/spool/emailrelay"
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* reject connections from remote clients
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* disable the administration interface
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* generate no logging or diagnostic messages
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To foward spooled messages to the ISP the command-line switch "--as-client"
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is provided to run the program...
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* in foreground, exiting when all spooled mail has been processed
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* forwarding spooled mail from "/usr/local/var/spool/emailrelay"
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* without listening on any port
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* with error, warning and information messages sent to stderr
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* without using syslog
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The "--as-server" switch makes sure that logging is enabled and that
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the standard error stream is closed.
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Message store
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-------------
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Mail messages are stored as text files in the configured spool directory. Each
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message is represented as an envelope file and a content file. The envelope
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file contains parameters relevant to the SMTP dialogue, and the content file
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contains the RFC822 headers and body text. Note that the content is largely
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ignored by the SMTP protocol.
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The filenames used in the message store have a prefix of "emailrelay", followed
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by a process-id and sequence number, followed by "envelope" or "content". The
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envelope files then have an additional suffix to implement a simple locking
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scheme.
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The envelope suffixes are:
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* ".new" -- while the envelope is first being written
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* <none> -- while the message is spooled
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* ".busy" -- while the message is being forwarded
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* ".bad" -- if the message cannot be forwarded
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* ".local" -- for copies of the envelope file for delivery to local recipeints
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Copies of the content file for delivery to local recipeints will also have
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a "local" suffix.
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If a message cannot be forwarded the envelope file is given a "bad" suffix,
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and the failure reason is written into the file.
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SMTP issues
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-----------
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Local delivery:
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E-MailRelay will reject all local recipients, with the exception of "postmaster".
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This is in line with its intended purpose as a simple mail relay, rather than
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a fully-fledged routing MTA. Any addressee (except "postmaster") without an "at"
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sign (@) will be rejected at the time the message is submitted by the e-mail
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front-end.
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Delivery of mail to a local "postmaster" is a feature of E-MailRelay which is
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provided for completeness and for comformance to the SMTP specification. It is
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only relevant if you are in the habit of sending mail to yourself as "postmaster";
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mail to "postmaster" from an external source is not processed by E-MailRelay
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and should be delivered normally.
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Note that E-MailRelay daemon does not actually deliver mail to the postmaster
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mailbox. All it does is create an envelope and content file in the spool directory
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with a ".local" suffix. Some external system, such as a shell script run
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from cron calling "procmail", should be used to process the ".local" files.
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An example script is provided.
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Timeouts:
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Client-side timeouts are not implemented. If the ISP server is very slow then
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in a typical setup the dial-up line will be dropped due to inactivity. This
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will have the desired effect of aborting the message submission.
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Message loops:
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Message loops are not detected.
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Eight bit messages:
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The 8BITMIME SMTP extension is supported, however no attempt is made to
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re-encode 8-bit messages into 7-bit messages if the downstream server
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does not.
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Administration interface
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------------------------
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If enabled, the server will provide a network interface for performing administration
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tasks. This is a simple command-line interface which is compatible with telnet.
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Currently the only supported command is "flush", which tries to forward spooled mail
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to the configured dowstream SMTP server. The downstream server address must have been
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defined on the "emailrelay" command line at start-up using the "--forward-to" switch;
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it cannot be specified through the administration interface.
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Security issues
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---------------
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E-MailRelay runs with a umask of 177. It does not call exec() or system(). It does not
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change its effective userid. No configuration parameters can be changed through the
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administrative interface. By default connections to the SMTP and administrative ports
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will be rejected if they come from remote machines.
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Files
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-----
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By default "make install" installs the following files:
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* /usr/local/sbin/emailrelay
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* /usr/local/libexec/emailrelay-poke
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* /usr/local/libexec/emailrelay.sh
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* /usr/local/var/spool/emailrelay/empty_file
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* /usr/local/share/emailrelay/emailrelay-notify.sh
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* /usr/local/share/emailrelay/emailrelay-deliver.sh
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This directory structure is constrained by the autoconf and GNU standards. Preferred
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locations would be something like this:
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* /usr/sbin/emailrelay
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* /opt/emailrelay/bin/emailrelay-poke
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* /sbin/init.d/emailrelay.sh
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* /var/spool/emailrelay/
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* /opt/emailrelay/examples/emailrelay-notify.sh
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* /opt/emailrelay/examples/emailrelay-deliver.sh
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Copyright (C) 2001 Graeme Walker <graeme_walker@users.sourceforge.net>. All rights reserved.
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