Provided by: courier-mta_0.60.0-2ubuntu1_i386
dotforward, dot-forward - Read $HOME/.forward
$ cat $HOME/.courier
The dotforward program is a compatibility module that reads forwarding
instructions in $HOME/.forward. dotforward is used for compatibility
with sendmail or other mail servers that use the $HOME/.forward file.
The dotforward program is intended to be executed from a
dot-courier(5) delivery instruction file. The system administrator
can add it to the default set of delivery instructions, thus
unilaterally implementing $HOME/.forward systemwide. To read forwarding
instructions from $HOME/.forward, put "|| dotforward" on the first line
of $HOME/.courier*. "|| dotforward" can also be added to the
DEFAULTDELIVERY setting in the courierd configuration file. In both
cases it must be followed by a newline, and the remaining delivery
instructions, which will be used if $HOME/.forward does not exist.
dotforward expects to be invoked from dot-courier(5) delivery
instruction file via the "||" operator (or from DEFAULTDELIVERY).
dotforward checks its environment, reads the message from standard
input, reconciles its environment with the contents of $HOME/.forward,
then prints on standard output equivalent dot-courier(5) compatible
delivery instructions. The "||" operator reinterprets dotforward’s
output as additional delivery instructions, by Courier.
The different security models of Courier and other mail servers that
use $HOME/.forward, such as sendmail, means that it is not possible to
faithfully duplicate 100% of the behavior of $HOME/.forward that
originated with sendmail. The following section documents the behavior
of the dotforward utility in the Courier mail server.
dotforward reads the DTLINE environment variable, and the headers of
the message being delivered, from standard input. DTLINE contains the
recipient’s E-mail address. The Delivered-To headers list the
recipients that already received this message. This is used to prevent
mail loops between $HOME/.forward files from different recipients,
which forward mail to each other.
If $HOME/.forward does not exist, dotforward quietly terminates with a
zero exit code, doing nothing. The remaining delivery instructions in
$HOME/.courier are then carried out.
If $HOME/.forward exists, it is expected to contain a list of addresses
that the message should be forwarded to. An address may be an actual
E-mail address, or a name of a program or a mailbox. Each line in
$HOME/.forward should contain a list of comma-separated addresses. Use
"| /path/to/program" (including the double quotes) to specify a
delivery to a program (the message is piped to the given program). Use
"/path/to/mailbox" or "./path/to/mailbox" (again including the double
quotes) to specify a delivery to a mailbox (relative to $HOME in the
"| /path/to/program", "/path/to/mailbox", and "./path/to/mailbox" may
also be listed on a line by themselves without the double quotes.
All other addresses are interpreted as E-mail addresses where the mail
should be forwarded. Any backslash at the beginning of an E-mail
address is removed. Backslashes are used by sendmail to prevent mail
loops. Courier does not need the backslashes -- it uses a different
mechanism to prevent mail loops.
Every E-mail address is checked against the list of E-mail addresses
found in Delivered-To headers. If the E-mail address specified in
$HOME/.forward matches any address in the Delivered-To header, it is
automatically removed from a list of addresses.
dotforward normally terminates with the exit code set to 99. This
results in Courier considering the message to be succesfully delivered,
and any additional delivery instructions in the .courier file will not
be carried out. If an address read from $HOME/.forward matches the
address in the DTLINE environment variable, the address is removed from
the list of addresses that the message will be forwarded to, and
dotforward terminates with the exit code set to 0 (after printing all
the relevant delivery instructions to standard output). The messages
will be forwarded, and Courier will proceed with additional delivery
instructions in the .courier after finishing with the delivery
instructions it reads from dotforward.
The restrictions and precautions mentioned in dot-courier(5) are
also applicable here. There is an upper limit on the maximum number of
characters that are read from any process executed by ||. Also if any
delivery instruction fails with a transit exit code, the message will
be completely redelivered at a later point, even to all the addresses
it has been succesfully delivered the first time around.