At times it is desirable to run sendmail so that it does not perform aliasing. When aliasing is disabled, sendmail uses the recipient address as is. No addresses are ever looked up in the aliases file, even if they are local.
The -n
command-line switch tells sendmail not to
perform aliasing of recipient addresses. This switch
is rarely used but can be handy in a couple of situations.
In tracking down delivery problems, it can be difficult to determine where the problem lies. If you suspect a bad alias, you can force aliasing to be skipped and see whether that causes the problem to go away:
%/usr/lib/sendmail -n user < /dev/null
This tells sendmail to send an empty mail message (one containing
mandatory headers only) to the recipient named user
. The
-n
prevents sendmail from looking up user
either in the aliases database or in ~/.forward.
If user
resolves to the local
delivery agent,
the message will be delivered, and you should therefore suspect an
aliasing problem.
Other switches, such as -v
(verbose) and
-d
(debugging), can be combined with -n
to view the delivery process in more detail.
The -n
command-line switch can also be used to suppress
aliasing when delivering to a list of recipients that has already
been aliased. For example, consider the following
script, which attempts to restrict delivery to users who have
mail delivered locally and to skip users who have mail forwarded
offsite:
#!/bin/sh EX_OK=0 # From <sysexits.h> EX_NOUSER=67 # From <sysexits.h> EX_SOFTWARE=70 # From <sysexits.h> if [ ${#} -ne 2 ]; then echo Usage: $0 list-name exit $EX_USAGE fi trap "exit 70" 1 2 13 15 LIST= "`/usr/lib/sendmail -bv $1 \ | grep "mailer local" 2>&1`" \ | sed 's/\\.\\.\\..*$//' if [ -z "$LIST" ] echo "$1 expanded to an empty list" exit $EX_NOUSER fi if /usr/lib/sendmail -n $LIST >/dev/null 2>&1 then exit $EX_OK fi exit $EX_SOFTWARE
The sendmail program is called twice inside this script. First, it
is given the -bv
switch,
which causes it to expand the list of recipients
in $1
. That expansion includes
aliasing (and ~/.forward
aliasing) for each name in the list. The output produced looks like
this:
user1... deliverable: mailer local, user user1 user2@otherhost... deliverable: mailer smtp, host otherhost, user user2@otherhost
The grep(1) program selects only those lines that
contain the expression "mailer local"
, thus indicating a
local user.
The sed(1) program then discards from the ... to the end
of each selected line.
The result, a list of local recipients only, is saved in the shell variable
LIST
.
The sendmail program is called with the -n
switch,
which prevents it from re-aliasing the list of names in
$LIST
(they have already been aliased once).
Note that this script should not be used as is because it checks only for the delivery
agent named local
, rather than for any delivery agent that can
perform final delivery.