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A no-dependence external policy checker for Postfix that does SPF and greylisting.
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tumgreyspf README Sean Reifschneider <email@example.com> Homepage: http://www.tummy.com/Community/software/tumgreyspf/ Code/bugfixes: https://github.com/linsomniac/tumgreyspf ============================================================= This is tumgreyspf, an external policy checker for the postfix mail server. It can optionally greylist and/or use spfquery to check SPF records to determine if email should be accepted by your server. It uses the file-system as it's database, no additional database is required to use it. LICENSE tumgreyspf is licensed under the GPL. BENEFITS High Accuracy SPF is information published by the domain owner about what systems may legitimately send e-mail for the domain. Greylisting takes advantage of spam and viruses that do not follow the RFCs and retry deliveries on temporary failure. We use these checks as part of our mail system and have seen several orders of magnitude reduction in spam, lower system load, and few problems with legitimate mail getting blocked. Low Maintenance tumgreyspf requires no regular attention from the administrator to remain effective. Easy Setup Installation should be as easy as installing an RPM or Debian package on your system. There are few additional requirements. Extensive time has been devoted to installation automation and documentation. REQUIREMENTS Python http://www.python.org/ Postfix 2.1 or above http://www.postfix.org/ Optional: spfquery or pyspf http://www.libspf2.org/ http://spf.pobox.com/downloads.html http://www.wayforward.net/spf/ NOTE BEFORE YOU USE TUMGREYSPF tumgreyspf stores the greylist data in the file-system using many small files. This has a few benefits, namely that you do not need to install or configure any database software. It also makes you immune to to database corruption issues that other greylist systems have. However, this does mean that if not configured properly you may experience extremely poor performance. There are details in one of my blog posts: http://www.tummy.com/blogs/2005/10/01/tumgreyspf-considered-useful/ However, the short answer is that you need to be careful about blocking known bad recipient and sender addresses in Postfix before handing messages off to tumgreyspf, and you probably should configure SPF to be checked before greylisting. If you are going to be storing your tumgreyspf database on an "ext2" or "ext3" file-system, you have to be particularly careful about this problem. I have run a number of production e-mail servers using this with extremely good results and absolutely no problems, however I do acknowledge that there is a potential for problems. Read the above URL for more details on preventing these problems. Over the last 18 months that it's been in use, and more than a year that it's been publicly available, I've received many responses saying that it worked great, and one blog post reporting the above problems. tumgreyspf may not be for everyone, but many people do find it useful. QUICK-START INSTALL There is a script called "tumgreyspf-install" provided with this software. I have had a report that it didn't work, so I would recommend against running it, instead see the "INSTALL INSTRUCTIONS" section at the end of this document for manual installation instructions. The install process is fairly easy, requiring some simple changes to the Postfix configuration files. LOGGING tumgreyspf will log messages to syslog about it's activities. The "debugLevel" value in "tumgreyspf.conf" can be increased to get additional information to be logged. When set to a value of "0", only test results (greylist/SPF hits/misses) are logged. Look for "tumgreyspf" in your mail log files. TESTING The best way to test tumgreyspf is to simulate SMTP connections, then watch the logs and look in the ".../data/" directory for greylist settings. This testing probably needs to be done from a remote system. For example, suppose we have a machine "10.9.8.7" that we want to run tests against our mail server "10.1.2.3": Log into 10.9.8.7. Run "telnet 10.1.2.3 25" Type "helo example.com" Type "mail from: <firstname.lastname@example.org>" Type "rcpt to: <email@example.com>" Note that "firstname.lastname@example.org" needs to be a valid local e-mail address in most cases, and that "email@example.com" is subject to SPF blocking. The first time you do this, you should receive the response: 450 <firstname.lastname@example.org>: Recipient address rejected: Service unavailable, greylisted. This indicates that the greylisting is working. Check the logs, you should see something similar to: Aug 22 19:52:49 mail tumgreyspf: Initial greylisting: REMOTEIP="10.9.8.7" HELO="example.com" SENDER="email@example.com" RECIPIENT="firstname.lastname@example.org" QUEUEID="" Aug 22 19:52:49 mail databytes: RCPT_INFO: REMOTEIP="10.9.8.7" HELO="example.com" SENDER="email@example.com" RECIPIENT="firstname.lastname@example.org" QUEUEID="" Aug 22 19:52:49 mail postfix/smtpd: NOQUEUE: reject: RCPT from testhost.example.com[10.9.8.7]: 450 <email@example.com>: Recipient address rejected: Service unavailable, greylisted.; from=<firstname.lastname@example.org> to=<email@example.com> proto=SMTP helo=<example.com> The "Initial greylisting" indicates that the record was not found in the database, and that a new entry was created. Now look in the greylist data for this entry: ls /firstname.lastname@example.orgemail@example.com Wait 10 minutes (or whatever you set the greylisting time to) and try it again. This time, in response to your "rcpt to" line, you should get: 250 Ok or (if you have enabled SPF blocking for your domain): 554 <firstname.lastname@example.org>: Recipient address rejected: Please see http://spf.pobox.com/why.html?sender=user2%40example.com&ip=10.9.8.7&receiver=spfquery The only way to get around the SPF block is to either disable SPF checking in tumgreyspf (perhaps for this IP only, see the "CONFIGURATION" section below), or change your SPF configuration so that it allows mail from your test machine. CONFIGURATION NOTE: After changing "tumgreyspf.conf", you should run "tumgreyspf-configtest" to ensure that it's correct. This only applies to changes made to the "tumgreyspf.conf" master configuration file. Configurations are processed from the top down, in the order specified by "OTHERCONFIGS". So, settings in a top-level __default__ file will be overridden if set in a configuration below that top level. There is the __default__ file at the top level that is used as a default for all decisions. If you wish to disable SPF or greylist for a specific IP/subnet/sender/recipient, you simply make a __default__ file in a subdirectory under config matching the entity you wish to match, with SPF or other checks disabled. For example, if you want to disable SPF queries for hosts in 192.168.10.0/24: mkdir /var/spool/tumgreyspf/config/client_address/192/168/10/ edit /var/spool/tumgreyspf/config/client_address/192/168/10/__default__ The __default__ file should contain: SPFSEEDONLY=0 GREYLISTTIME=300 CHECKERS= OTHERCONFIGS= Note that for a specific IP address, the last component is a file, having the same structure as the __default__. For example, to block the address "10.1.2.3", you would create a file named "3" under the directory ".../config/client_address/10/1/2". The above sets CHECKERS and OTHERCONFIGS to nothing, so for that subnet no checks are done. All other IP address blocks are still using the top level __default__ CONFIGURATION VALUES SPFSEEDONLY=1 will only check SPF, not use it for decisions. GREYLISTTIME is the number of seconds to wait before allowing a an incoming message. Unless you have a good reason for it, this should never be more than 3 hours or it may cause warnings about undeliverable e-mail to be sent. CHECKERS is one of the set of 'spf' and 'greylist'. This is a list of checks to perform. Note that they are done in the listed order. OTHERCONFIGS specifies which configurations will be used. Note that these configurations are read a maximum of once, and are applied in order. If another configuration changes this list, any configurations that are already done will be skipped. Allowed values are: client_address Look for configuration values based on the remote IP address. For example, if the remote host "10.9.8.7" is connecting, the following will be tried: .../config/client_address/10/__default__ .../config/client_address/10/9/__default__ .../config/client_address/10/9/8/__default__ .../config/client_address/10/9/8/7 envelope_sender Split the envelope sender (not the header "From" address) into "domain" and "local" parts, and look for a domain-specific configuration, or a configuration specific to a particular sender. So, if "email@example.com" sends a message, the following files would be tried: .../config/envelope_sender/example.com/__default__ .../config/envelope_sender/example.com/user Note that special characters other than @, _ (underscore), - (dash), . (dot), and + (plus) are escaped using "%DD" format, where "DD" is the hex value of the ASCII character. Also note that a leading "." in a domain or user is converted to "%2e", to prevent the confusion of "hidden files". envelope_recipient This is handled the same as envelope_sender, but is the envelope recipient. Note that this is not the value of the "To" header in the message, but the value in the envelope. GREYLISTEXPIREDAYS is a floating point number of days since receiving the last piece of e-mail after which a greylist entry will be expired. This value is used by "tumgreyspf-clean". INSTALL INSTRUCTIONS The fastest way to install tumgreyspf is to use the package for your system. This will use "tumgreyspf-install" to attempt to automatically configure postfix for tumgreyspf. However, it's recommended that you carefully review the Postfix configuration changes and verify that they are as you expect. INSTALLING THE SOFTWARE This does not need to be done if you've installed the RPM/Debian package. tumgreyspf uses two directories. One is for the main tumgreyspf code, and the other is for it's data/configuration. I call these directories "$TGSPROG" and "$TGSDATA" in the instructions below. Additionally, the user which tumgreyspf runs as is "$TGSUSER". Run the following commands: TGSPROG=/usr/local/lib/tumgreyspf TGSDATA=/var/local/lib/tumgreyspf TGSUSER=nobody # set up directories mkdir -p "$TGSPROG" "$TGSDATA"/config mkdir "$TGSDATA"/data chown -R nobody "$TGSDATA"/data cp __default__.dist "$TGSDATA"/config/__default__ # install programs cp tumgreyspf tumgreyspf-clean tumgreyspf-configtest "$TGSPROG" cp tumgreyspf-install tumgreyspf-stat tumgreyspfsupp.py "$TGSPROG" cp tumgreyspf.conf "$TGSDATA"/config/ # change permissions and ownership chown -R "$TGSUSER" "$TGSDATA" chown -R root "$TGSPROG" "$TGSDATA"/config chmod 700 "$TGSDATA"/data chmod -R 755 "$TGSDATA"/config If you have changed the values of TGSPROG or TGSDATA, you will need to change the the paths in the following files. In the .conf file, you will need to review the whole file, the other files have the required changes isolated to the top of the file: "$TGSDATA"/config/tumgreyspf.conf "$TGSPROG"/tumgreyspfsupp.py "$TGSPROG"/tumgreyspf "$TGSPROG"/tumgreyspf-clean "$TGSPROG"/tumgreyspf-stat CRONTAB WARNING: Make *SURE* you do this step, as not cleaning out the database may result in resource exhaustion in your file-system. Next, you will need to add a cron job which runs daily to clean out the the expired SPF entries. On many systems, there is a "/etc/cron.d" directory, and the following can be be used to add an entry: echo 0 0 * * * $TGSUSER $TGSPROG/tumgreyspf-clean \ >/etc/cron.d/tumgreyspf Otherwise, you will need to use "crontab -e -u $TGSUSER" to add the following entry: 0 0 * * * $TGSPROG/tumgreyspf-clean Note that you cannot use the literal "$TGSPROG", you will have to replace it with whatever the real value is. CONFIGURING POSTFIX WARNING: In these examples, you cannot use the literal "$TGS" variables. You will have to manually replace the appropriate values, they are simply there to mark where the changes need to be. Add to your postfix master.cf: tumgreyspf unix - n n - - spawn user=nobody argv=$TGSPROG/tumgreyspf Next, main.cf must be configured so that "smtpd_recipient_restrictions" includes a call to the tumgreyspf policy filter. If you already have a "smtpd_recipient_restrictions" line(s), you can add the following line anywhere after the line which reads "reject_unauth_destination". check_policy_service unix:private/tumgreyspf WARNING: It's very important that you have "reject_unauth_destination" before the "check_policy_service". If you do not, your system may be an open relay. So, for example, a minimal "smtpd_recipient_restrictions" may look like: smtpd_recipient_restrictions = \ reject_unauth_destination, \ check_policy_service unix:private/tumgreyspf Please consult the postfix documentation for more information on these and other settings you may wish to have in the "smtpd_recipient_restrictions" configuration. You will also need to have a line in the main.cf which reads: tumgreyspf_time_limit = 3600 SPF INSTALLATION NOTE: SPF is optional, but it's use, particularly it's use before greylisting, will help reduce spam and will reduce the size of the greylist database. This may prevent or lessen the problems mentioned in the "NOTE BEFORE YOU USE TUMGREYSPF" section. tumgreyspf can also use an external SPF program to do SPF lookups. You can use any of the following: Download libspf2 from http://www.libspf2.org/ untar and run "./configure; make", then copy "src/spfquery/spfquery_static" to "$TGSPROG". The Mail::SPF::Query Perl module includes a "spfquery" package that tumgreyspf can be used with. Once installed, change your tumgreyspf.conf file to list the path to "spfquery". Information on downloading this package is available from http://spf.pobox.com/downloads.html The Python pyspf package from http://www.wayforward.net/spf/ can also be used. If this is installed, tumgreyspf will automatically use it. COMMON PROBLEMS SPF checks need to be bypassed for relays for the domain, such as secondary MX servers. Putting an mx entry in your SPF TXT record is not sufficient to do this, as that only covers your *OUTGOING* e-mail. Incoming e-mail is controlled by the senders SPF record, which probably doesn't list your secondary MX hosts. :-) One way of bypassing this check would be to ensure that MX servers are listed in mynetworks, and that permit_mynetworks is ahead of the call to tumgreyspf.