Compiling Python Milter
- Q. I have installed sendmail from source, but Python milter won't
compile.
A. Even though libmilter is officially supported in sendmail-8.12,
you need to build and install it in separate steps. Take a look
at the RPM spec file for sendmail-8.12.
The %prep section shows you how to create
a site.config.m4 that enables MILTER. The %build section shows you how
to build libmilter in a separate invocation of make. The %install section
shows you how to install libmilter with a separate invocation of make.
- Q. Why is mfapi.h not found when I try to compile Python milter on
RedHat 7.2?
A. RedHat forgot to include the header in the RPM. See the
RedHat 7.2 requirements.
- Q. Python milter compiles ok, but I get an error like this when
I try to import the milter module:
ImportError: /usr/lib/python2.4/site-packages/milter.so: undefined symbol: smfi_setmlreply
A. Your libmilter.a is from sendmail-8.12 or earlier. You need
sendmail-8.13 or later to support setmlreply. You can disable
setmlreply by changing setup.py. Change:
define_macros = [ ('MAX_ML_REPLY',32) ]
in setup.py to
define_macros = [ ('MAX_ML_REPLY',1) ]
Running Python Milter
- Q. The sample.py milter prints a message, then just sits there.
To use this with sendmail, add the following to sendmail.cf:
O InputMailFilters=pythonfilter
Xpythonfilter, S=local:inet:1030@localhost
See the sendmail README for libmilter.
sample milter startup
A. You need to tell sendmail to connect to your milter. The
sample milter tells you what to add to your sendmail.cf to tell
sendmail to use the milter. You can also add an INPUT_MAIL_FILTER
macro to your sendmail.mc file and rebuild sendmail.cf - see the sendmail
README for milters.
- Q. I've configured sendmail properly, but still nothing happens
when I send myself mail!
A. Sendmail only milters SMTP mail. Local mail is not miltered.
You can pipe a raw message through sendmail to test your milter:
$ cat rawtextmsg | sendmail myname@my.full.domain
Now check your milter log.
- Q. Why do I get this ImportError exception?
File "mime.py", line 370, in ?
from sgmllib import declstringlit, declname
ImportError: cannot import name declstringlit
A. declstringlit
is not provided by sgmllib in all versions
of python. For instance, python-2.2 does not have it. Upgrade to
milter-0.4.5 or later to remove this dependency.
- Q. Why do I get
milter.error: cannot add recipient
?
A. You must tell libmilter how you might mutate the message with
set_flags()
before calling runmilter()
. For
instance, Milter.set_flags(Milter.ADDRCPT)
. You must add together
all of ADDHDRS, CHGBODY, ADDRCPT, DELRCPT, CHGHDRS
that apply.
NOTE - recent versions default flags to enabling all features. You
must now call set_flags()
if you wish to disable features for
efficiency.
- Q. Why does sendmail sometimes print something like:
"...write(D) returned -1, expected 5: Broken pipe"
in the sendmail log?
A. Libmilter expects "rcpt to" shortly after getting "mail from".
"Shortly" is defined by the timeout parameter you passed to
Milter.runmilter()
or milter.settimeout()
. If the timeout is 10 seconds,
and looking up the first recipient in DNS takes more than
10 seconds, libmilter will give up and break the connection.
Milter.runmilter()
defaulted to 10 seconds in 0.3.4. In 0.3.5
it will keep the libmilter default of 2 hours.
- Q. Why does milter block messages with big5 encoding? What if I
want to receive them?
A. sample.py is a sample. It is supposed to be easily modified
for your specific needs. We will of course continue to move generic
code out of the sample as the project evolves. Think of sample.py as
an active config file.
If you are running bms.py, then the block_chinese option in
/etc/mail/pymilter.cfg
controls this feature.
- Q. Why does sendmail coredump with milters on OpenBSD?
A. Sendmail has a problem with unix sockets on old versions of OpenBSD.
OpenBSD users report that this problem has been fixed, so upgrading
OpenBSD will fix this. Otherwise, you can
use an internet domain socket instead. For example, in
sendmail.cf
use
Xpythonfilter, S=inet:1234@localhost
and change sample.py accordingly.
- Q. How can I change the bounce message for an invalid recipient?
I can only change the recipient in the eom callback, but the eom callback
is never called when the recipient is invalid!
A. Configure sendmail to use virtusertable, and send all unknown
addresses to /dev/null. For example,
/etc/mail/virtusertable
@mycorp.com dev-null
dan@mycorp.com dan
sally@mycorp.com sally
/etc/aliases
dev-null: /dev/null
Now your milter will get to the eom callback, and can change the
envelope recipient at will. Thanks to Dredd at
milter.org for this solution.
- Q. I am having trouble with the setreply method. It always outputs
"milter.error: cannot set reply".
A. Check the sendmail log for errors. If sendmail is getting
milter timeouts, then your milter is taking too long and sendmail gave
up waiting. You can adjust the timeouts in your sendmail config. Here
is a milter declaration for sendmail.cf with all timeouts specified:
Xpythonfilter, S=local:/var/log/milter/pythonsock, F=T, T=C:5m;S:20s;R:60s;E:5m
- Q. There is a Python traceback in the log file! What happened to
my email?
A. By default, when the milter fails with an untrapped exception, a
TEMPFAIL result (451) is returned to the sender. The sender will then retry
every hour or so for several days. Hopefully, someone will notice the
traceback, and workaround or fix the problem. Beginning with milter-0.8.2,
you can call milter.set_exception_policy(milter.CONTINUE)
to cause an untrapped exception to continue processing with the
next callback or milter instead. For
completeness, you can also set the exception policy to
milter.REJECT
.
- Q. I read some notes such as "Check valid domains allowed by internal
senders to detect PCs infected with spam trojans." but could not
understand the idea. Could you clarify the content ?
A. The internal_domains
configuration specifies which
MAIL FROM domains are used by internal connections. If an internal
PC tries to use some other domain, it is assumed to be a "Zombie".
Here is a sample log line:
2005Jun22 12:01:04 [12430] REJECT: zombie PC at 192.168.100.171 sending MAIL FROM debby@fedex.com
No, fedex.com does not use pymilter, and there is no one named debby at my
client. But the idiot using the PC at 192.168.100.171 has downloaded and
installed some stupid weatherbar/hotbar/aquariumscreensaver that is actually a
spam bot.
The internal_domains
option is simplistic, it assumes all
valid senders of the domains are internal. SPF provides a much more general
check of IP and MAIL FROM for external email. Pymilter should soon
have a local policy feature for more general checking of internal mail.
Using SPF
- Q. So how do I use the SPF support? The sample.py milter doesn't seem
to use it.
A. The bms.py milter supports spf. The RedHat RPMs will set almost
everything up for you. For other systems:
- Arrange to run bms.py in the background (as a service perhaps) and
redirect output and errors to a logfile. For instance, on AIX you'll want
to use SRC (System Resource Controller).
- Copy pymilter.cfg to the /etc/mail or the directory you run bms.py in,
and edit it. The comments should explain the options.
- Start bms.py in the background as arranged.
- Add Xpythonfilter to sendmail.cf or add an INPUT_MAIL_FILTER to
sendmail.mc. Regen sendmail.cf if you use sendmail.mc and restart
sendmail.
- Arrange to rotate log files and remove old defang files in
tempdir
. The RedHat RPM uses logrotate
for
logfiles and a simple cron script using find
to clean
tempdir
.