qmail/moreipme.README

###########
### WHO ###
###########

This patch was written by Scott Gifford <sgifford@suspectclass.com>.
The design and much of the code for supporting "notipme" was
contributed by Charles Cazabon <charlesc@discworld.dyndns.org>.


############
### WHAT ###
############

This patch may be necessary in some configurations that involve network
address translation or port forwarding.  It prevents a problem caused
by an MX or other mail routing directive instructing qmail to connect to
itself without realizing it's connecting to itself.  When this happens,
it accepts the message, finds out where to deliver it to (itself), and
promptly reconnects to itself to deliver the message.  Eventually, when
it has done this 20 or 30 times, it will give up and bounce the message,
but not before sucking up all of your CPU while it's happening.

It may also be useful in some configurations that have multiple qmail
servers configured on different interfaces of the same system.  qmail
will normally refuse to deliver mail by SMTP to the machine it's
running on, but with multiple copies of qmail, you may want to prevent
this behavior.

Normally, qmail can detect what IP addresses refer to itself by getting
a list of all network interfaces with IP addresses from the operating
system.  It uses this list to determine whether connecting to an address
will cause it to connect to itself, and avoid the situation (it calls
the perm_ambigmx() function, which prints the message:

   Sorry. Although I'm listed as a best-preference MX or A for that host,
   it isn't in my control/locals file, so I don't treat it as local. (#5.4.6)

But in situations where the OS is not aware of all IP addresses that
connect back to itself, this detection fails, causing the CPU-sucking
phenomenon described above.  This can happen if there is a network
address translation device in front of the qmail server, such as a
load-balancer or a router which allows you to share one IP address among
several machines; if there is a port forwarder forwarding connections
from some other machine to the SMTP server on the qmail server; or in
configurations where a "dumb" mailserver is configured to use your qmail
server as a "smarthost", delivering all mail to it without inspection.

To solve this, other IP addresses which will ultimately connect back to
your machine can be added to the file "control/moreipme", one per line.
qmail will treat all addresses in this file exactly as if they were
local, and if it finds an MX record or other mail routing information
which would cause it to connect to any of these addresses, it will call
perm_ambigmx(), and print the above error message.

Additionally, IP addresses which the system detects but which should
*not* be treated as local can be removed from qmail's ipme list by
adding them to the file "control/notipme".

IP addresses can be specified as individual addresses in the usual
dotted-quad format, or as entire networks using a slash followed by
the full dotted-quad netmask:

    127.0.0.1
    127.0.0.1/255.255.255.255
    127.0.0.0/255.0.0.0
    10.0.0.0/255.255.255.0

An individual address is treated exactly like a network with a mask of
255.255.255.255.  Addresses of interfaces found on the system are
added with their individual addresses.  In addition, these addresses
are implicitly added:

    0.0.0.0
    127.0.0.0/255.0.0.0

So the list of system addresses (the "ipme" list) is, in order,
127.0.0.0/255.0.0.0, 0.0.0.0, then all actual interfaces on the system
in the order they are reported, then the contents of the "moreipme"
file.  The list of excluded addresses (the "notipme" list) is just the
contents of the "notipme" file.

If an address appears in both the ipme list and the notipme list, the
entry with the longest netmask wins.  If the netmask lengths are the
same, notipme wins.

For example, if the ipme list has 127.0.0.0/255.0.0.0 and notipme has
127.0.0.2, then 127.0.0.2 will not be considered me because the entry
in notipme has a 32-bit mask.  If the notipme list has
127.0.0.0/255.0.0.0, all of 127.* will not be considered me.

You can run the program "ipmeprint" from the source directory to see
what interfaces qmail is detecting or finds in moreipme.

You can run the program "ipmetest" from the source directory to test
your configuration.  It takes as its first and only parameter an IP
address to test, and prints either "me" or "not me".

###########
### HOW ###
###########

To apply the patch, download and save it somewhere, then cd into your
qmail source directory.

For stock qmail, download qmail-1.03-moreipme-0.6.patch then run:

    cd qmail-1.03
    patch -p1 </path/to/qmail-1.03-moreipme-0.6.patch

For netqmail, first download netqmail-1.05, and run the included
collate.sh script.  Then download netqmail-1.05-moreipme-0.6.patch and
apply it to the netqmail base directory, after runn:

    cd netqmail-1.05
    patch -p1 </path/to/netqmail-1.05-moreipme-0.6.patch
 

###################
### OTHER NOTES ###
###################

This patch also incorporates the "0.0.0.0" patch, which causes qmail 
to recognize the IP address 0.0.0.0 as a local address.  See:

    http://www.suspectclass.com/~sgifford/qmail/qmail-0.0.0.0.README

for more information, and

    http://www.suspectclass.com/~sgifford/qmail/qmail-0.0.0.0.patch

for a copy of the patch.


###############
### HISTORY ###
###############

2004 May 22 - Patch version 0.6 released.  Fix from Richard Dawe where
              masks weren't handled properly, removed some dead code,
              updated comments and docs.  Produce a copy of the patch
              for netqmail-1.05.

2003 Apr 29 - Patch version 0.5 released.  Added support for netmasks
              in moreipme and notipme, ipmetest utility, 127/8 as
              implicit ipme.

2002 Apr 26 - Patch version 0.4 released.  Includes support for "notipme" file.
              Many other small fixes and cleanups.  Fixes ipmeprint to
              chdir(/var/qmail) before running.

2001 Oct  8 - Original release of patch.

2001 Jan 22 - (roughly) Original release of 0.0.0.0 patch.