It can instead write the mail to a different file or directory, forward it to another address, distribute it to a mailing list, or even execute programs, all under your control.
.qmail contains one or more lines. Each line is a delivery instruction. qmail-local follows each instruction in turn. There are five types of delivery instructions: (1) comment; (2) program; (3) forward; (4) mbox; (5) maildir.
# this is a comment
qmail-local ignores the line.
|preline /usr/ucb/vacation djb
qmail-local takes the rest of the line as a command to supply to sh. See qmail-command(8) for further information.
qmail-local takes the rest of the line as a mail address; it uses qmail-queue to forward the message to that address. The address must contain a fully qualified domain name; it must not contain extra spaces, angle brackets, or comments:
# the following examples are WRONG
&email@example.com (New Address)
If the address begins with a letter or number, you may leave out the ampersand:
Note that qmail-local omits its new Return-Path line when forwarding messages.
qmail-local takes the entire line as a filename. It appends the mail message to that file, using flock-style file locking if possible. qmail-local stores the mail message in mbox format, as described in mbox(5).
WARNING: On many systems, anyone who can read a file can flock it, and thus hold up qmail-local's delivery forever. Do not deliver mail to a publicly accessible file!
If qmail-local is able to lock the file, but has trouble writing to it (because, for example, the disk is full), it will truncate the file back to its original length. However, it cannot prevent mailbox corruption if the system crashes during delivery.
qmail-local takes the entire line as the name of a directory in maildir format. It reliably stores the incoming message in that directory. See maildir(5) for more details.
If .qmail has the execute bit set, it must not contain any program lines, mbox lines, or maildir lines. If qmail-local sees any such lines, it will stop and indicate a temporary failure.
If .qmail is completely empty (0 bytes long), or does not exist, qmail-local follows the defaultdelivery instructions set by your system administrator; normally defaultdelivery is ./Mailbox, so qmail-local appends the mail message to Mailbox in mbox format.
.qmail may contain extra spaces and tabs at the end of a line. Blank lines are allowed, but not for the first line of .qmail.
If .qmail is world-writable, qmail-local stops and indicates a temporary failure.
chmod +t $HOME
qmail-local will temporarily defer delivery of any message to you if your home directory is sticky (or group-writable or other-writable, which should never happen). Make sure to
chmod -t $HOME
when you are done! It's a good idea to test your new .qmail file as follows:
qmail-local -n $USER ~ $USER '' '' '' '' ./Mailbox
The alias user controls all other addresses. Delivery to local is controlled by the file homedir/.qmail-local, where homedir is alias's home directory.
In the following description, qmail-local is handling a message addressed to local@domain, where local is controlled by .qmail-ext. Here is what it does.
If .qmail-ext is completely empty, qmail-local follows the defaultdelivery instructions set by your system administrator.
If .qmail-ext doesn't exist, qmail-local will try some default .qmail files. For example, if ext is foo-bar, qmail-local will try first .qmail-foo-bar, then .qmail-foo-default, and finally .qmail-default. If none of these exist, qmail-local will bounce the message. (Exception: for the basic user address, qmail-local treats a nonexistent .qmail the same as an empty .qmail.)
WARNING: For security, qmail-local replaces any dots in ext with colons before checking .qmail-ext. For convenience, qmail-local converts any uppercase letters in ext to lowercase.
When qmail-local forwards a message as instructed in .qmail-ext (or .qmail-default), it checks whether .qmail-ext-owner exists. If so, it uses local-owner@domain as the envelope sender for the forwarded message. Otherwise it retains the envelope sender of the original message. Exception: qmail-local always retains the original envelope sender if it is the empty address or #@, i.e., if this is a bounce message.
qmail-local also supports variable envelope return paths (VERPs): if .qmail-ext-owner and .qmail-ext-owner-default both exist, it uses local-owner-@domain-@ as the envelope sender. This will cause a recipient recip@reciphost to see an envelope sender of local-owner-recip=reciphost@domain.
If a program returns exit code 99, qmail-local ignores all succeeding lines in .qmail, but it still pays attention to previous forward lines.
To set up independent instructions, where a temporary or permanent failure in one instruction does not affect the others, move each instruction into a separate .qmail-ext file, and set up a central .qmail file that forwards to all of the .qmail-exts. Note that qmail-local can handle any number of forward lines simultaneously.