Rmilter

Synopsis

rmilter [-h ] [-c config_file ]

Description

The rmilter utility is designed to act as milter for sendmail and postfix MTA. It provides several filter and mail scan features, among them are:

• Clamav scanning (via unix or tcp socket).
• Spamassasin scanning
• Spf checking (via libspf2)
• Greylisting with memcached upstream
• Ratelimit with memcached upstream
• Auto-whitelisting (internal and via memcached upstream)
• Regexp checks.
• DCC checking (optional)
• Passing messages and/or their headers to beanstalk servers

The following additional options are supported:

• -h: Show greeting message, version of rmilter and exit
• -c config_file: Specify config file to use

All rmilter configuration is placed in rmilter.conf file.

Configuration format

The configuration file has format:

name = value ;

Value may be:

• String (may not contain spaces)
• Quoted string (if string may contain spaces)
• Numeric value
• Flag (y, Yes or n, No)
• IPv4 or network (eg. 127.0.0.1, 192.168.1.0/24)
• Socket argument (eg. host:port or /path/to/socket)
• Regexp (eg. /Match\*/)
• List (eg. value1, value2, value3)
• Recipients list (user, user@domain, @domain)
• Time argument (eg. 10s, 5d)

Some directives MUST be specified only in specified sections. Section definition looks like:

section_name {
        section_directive;
        ...
};

Common sections:

• clamav - clamav definitions
• spamd - spamassassin definitions
• limits - limits definitions
• greylisting - greylisting definitions
• rule - regexp rule definition (a section per rule)

Directives that can be defined in config file:

• Global section:

  • pidfile: specify path to pidfile

    Default: /var/run/rmilter.pid

  • tempdir: specify path to temporary directory. For maximum performance it is recommended to put it on memory file system.

    Default: $TMPDIR

  • bind_socket: socket credits for local bind:

    1. unix:/path/to/file - bind to local socket
    2. inet:[port@host] - bind to inet socket

    Default: bind_socket = unix:/var/tmp/rmilter.sock

  • max_size: maximum size of scanned message for clamav, spamd and dcc.

    Default: 0 (no limit)

  • spf_domains: list of domains that would be checked with spf

    Default: empty (spf disabled)

  • use_dcc: flag that specify whether we should use dcc checks for mail

    Default: no

  • whitelist: global recipients whitelist

    Default: no

• Clamav section:

  • servers: clamav socket definitions in format:

    1. /path/to/file
    2. host[:port]

    Sockets are separated by ,

    Default: empty

  • connect_timeout: timeout in miliseconds for connecting to clamav

    Default: 1s

  • port_timeout: timeout in miliseconds for waiting for clamav port response

    Default: 4s

  • results_timeout: timeout in miliseconds for waiting for clamav response

    Default: 20s

  • error_time: time in seconds during which we are counting errors

    Default: 10

  • dead_time: time in seconds during which we are thinking that server is down

    Default: 300

  • maxerrors: maximum number of errors that can occur during error_time to make us thinking that this upstream is dead

    Default: 10

• Spamd section:

  • servers: spamd (or rspamd) socket definitions in format:

    1. /path/to/file
    2. host[:port]
    3. r:/path/to/file - for rspamd protocol
    4. r:host[:port] - for rspamd protocol

    Sockets are separated by ,.

    Default: empty (spam checks disabled)

  • connect_timeout: timeout in miliseconds for connecting to spamd

    Default: 1s

  • results_timeout: timeout in miliseconds for waiting for spamd response

    Default: 20s

  • error_time: time in seconds during which we are counting errors

    Default: 10

  • dead_time: time in seconds during which we are thinking that server is down

    Default: 300

  • maxerrors: maximum number of errors that can occur during error_time to make us thinking that this upstream is dead

    Default: 10

  • reject_message: reject message for spam (quoted string)

    *Default: Spam message rejected; If this is not spam contact abuse team

  • spamd_soft_fail: if action is not reject use it for other actions (flag)

    Default: true

  • spamd_greylist: greylist message only if action is greylist (flag)

    Default: true

  • spam_header: add specified header if action is add_header and spamd_soft_fail os turned on

    Default: **X-Spam''

  • rspamd_metric: rspamd metric that would define whether we reject message as spam or not (quoted string)

    Default: **default''

  • whitelist: list of ips or nets that should be not checked with spamd

    Default: empty

  • extended_spam_headers: add extended spamd headers to messages, is useful for debugging or private mail servers (flag)

    Default: false

• Memcached section:

  • servers_grey: memcached servers for greylisting in format: host[:port][, host[:port]] It is possible to make memcached mirroring (for two servers only), its syntax is {server1,server2}

    Default: empty

  • servers_white: memcached servers for whitelisting in format similar to that is used in servers_grey

    Default: empty

  • servers_limits: memcached servers used for limits storing, can not be mirrored

    Default: empty

  • connect_timeout: timeout in miliseconds for connecting to memcached

    Default: 1s

  • error_time: time in seconds during which we are counting errors

    Default: 10

  • dead_time: time in seconds during which we are thinking that server is down

    Default: 300

  • maxerrors: maximum number of errors that can occur during error_time to make us thinking that this upstream is dead

    Default: 10

  • protocol: protocol that is using for connecting to memcached (tcp or udp)

    Default: udp

• Beanstalk section:

  • servers: beanstalk servers for pushing headers in format: host[:port][, host:port]

    Default: empty

  • copy_server: address of server to which rmilter should send all messages copies

    Default: empty

  • spam_server: address of server to which rmilter should send spam messages copies

    Default: empty

  • connect_timeout: timeout in miliseconds for connecting to beanstalk

    Default: 1s

  • error_time: time in seconds during which we are counting errors

    Default: 10

  • dead_time: time in seconds during which we are thinking that server is down

    Default: 300

  • maxerrors: maximum number of errors that can occur during error_time to make us thinking that this upstream is dead

    Default: 10

  • id_regexp: regexp that defines for which messages we should put the whole message to beanstalk, not only headers, now this regexp checks only In-Reply-To headers

    Default: empty

  • send_beanstalk_headers: defines whether we should send headers to beanstalk servers (from servers option)

    Default: no

  • send_beanstalk_copy: defines whether we should send copy of messages to beanstalk server (from copy_server option)

    Default: no

  • send_beanstalk_spam: defines whether we should send copy of spam messages to beanstalk server (from spam_server option)

    Default: no

  • protocol: protocol that is using for connecting to beanstalk (tcp or udp)

    Default: tcp

• Greylisting section:

  • timeout (required): time during which we mark message greylisted

    Default: 300s

  • expire (required): time during which we save a greylisting record

    Default: empty (greylisting disabled)

  • whitelist: list of ip addresses or networks that should be whitelisted from greylisting

    Default: empty

  • awl_enable: enable internal auto-whitelist mechanics

    Default: no

  • awl_pool: size for in-memory auto whitelist

    Default: 10M

  • awl_hits: number of messages (from this ip) that passes greylisting to put this ip into whitelist

    Default: 10

  • awl_ttl: time to live for ip address in auto whitelist

    Default: 3600s

• Limits section.

  Rate limits are implemented as leaked bucket, so first value is bucket burst - is peak value for messages in bucket (after reaching it bucket is counted as overflowed and new messages are rejected), second value is rate (how much messages can be removed from bucket each second). It can be schematically displayed:

          |------------------|          <----- current value
          |                  |
          |------------------|          <----- burst
          |                  |
          |                  |
          |                  |
          |                  |
          \                  /
           ----------------- .....      <----- rate (speed of emptying)
  

  • limit_whitelist_ip: don't check limits for specified ips

    Default: empty

  • limit_whitelist_rcpt: don't check limits for specified recipients

    Default: no

  • limit_bounce_addrs: list of address that require more strict limits

    Default: postmaster, mailer-daemon, symantec_antivirus_for_smtp_gateways, null, fetchmail-daemon

  • limit_bounce_to: limits bucket for bounce messages (only rcpt to)

    Default: 5:0.000277778

  • limit_bounce_to_ip: limits bucket for bounce messages (only rcpt to per one source ip)

    Default: 5:0.000277778

  • limit_to: limits bucket for non-bounce messages (only rcpt to)

    Default: 20:0.016666667

  • limit_to_ip: limits bucket for non-bounce messages (only rcpt to per one source ip)

    Default: 30:0.025

  • limit_to_ip_from: limits bucket for non-bounce messages (msg from, rcpt to per one source ip)

    Default: 100:0.033333333

• DKIM section.

  Dkim can be used to sign messages by. Dkim support must be provided with opendkim library and rmilter must be configured with --enable-dkim option.

  • header_canon: canonization of headers (simple or relaxed)

    Default: simple

  • body_canon: canonization of body (simple or relaxed)

    Default: simple

  • sign_alg: signature algorithm (sha1 for rsa-sha1 and sha256 for rsa-sha256)

    Default: sha1

  • auth_only: sign mail for authorized users only

    Default: yes

  • domain: domain entry must be enclosed in braces {}

  • key - path to private key

  • domain - domain to be used for signing (this matches with SMTP FROM data)

  • selector - dkim DNS selector (e.g. for selector dkim and domain example.com DNS TXT record should be for dkim._domainkey.example.com).

Example configuration

# pidfile - path to pid file
# Default: pidfile = /var/run/rmilter.pid

pidfile = /var/run/rmilter/rmilter.pid;


clamav {
        # servers - clamav socket definitions in format:
        # /path/to/file
        # host[:port]
        # sockets are separated by ','
        # Default: empty
        servers = clamav.test.ru, clamav.test.ru, clamav.test.ru;
        # connect_timeout - timeout in miliseconds for connecting to clamav
        # Default: 1s
        connect_timeout = 1s;

        # port_timeout - timeout in miliseconds for waiting for clamav port response
        # Default: 4s
        port_timeout = 4s;

        # results_timeout - timeout in miliseconds for waiting for clamav response
        # Default: 20s
        results_timeout = 20s;

        # error_time - time in seconds during which we are counting errors
        # Default: 10
        error_time = 10;

        # dead_time - time in seconds during which we are thinking that server is down
        # Default: 300
        dead_time = 300;

        # maxerrors - maximum number of errors that can occur during error_time to make us thinking that 
        # this upstream is dead
        # Default: 10
        maxerrors = 10;
};

spamd {
        # servers - spamd socket definitions in format:
        # /path/to/file
        # host[:port]
        # sockets are separated by ','
        # Default: empty
        servers = r:localhost:11333;
        # connect_timeout - timeout in miliseconds for connecting to spamd
        # Default: 1s
        connect_timeout = 1s;

        # results_timeout - timeout in miliseconds for waiting for spamd response
        # Default: 20s
        results_timeout = 20s;

        # error_time - time in seconds during which we are counting errors
        # Default: 10
        error_time = 10;

        # dead_time - time in seconds during which we are thinking that server is down
        # Default: 300
        dead_time = 300;

        # maxerrors - maximum number of errors that can occur during error_time to make us thinking that 
        # this upstream is dead
        # Default: 10
        maxerrors = 10;

        # reject_message - reject message for spam
        # Default: "Spam message rejected; If this is not spam contact abuse team"
        reject_message = "Spam message rejected; If this is not spam contact abuse team";

        # whitelist - list of ips or nets that should be not checked with spamd
        # Default: empty
        whitelist = 127.0.0.1/32, 192.168.0.0/16;
};

memcached {
        # servers_grey - memcached servers for greylisting in format:
        # host[:port][, host[:port]]
        # It is possible to make memcached mirroring, its syntax is {server1, server2}
        servers_grey = {localhost, memcached.test.ru}, memcached.test.ru:11211;

        # servers_white - memcached servers for whitelisting in format similar to that is used
        # in servers_grey
        # servers_white = {localhost, memcached.test.ru}, memcached.test.ru:11211;
        
        # servers_limits - memcached servers used for limits storing, can not be mirrored
        servers_limits = memcached.test.ru, memcached.test.ru:11211;

        # connect_timeout - timeout in miliseconds for waiting for memcached
        # Default: 1s
        connect_timeout = 1s;

        # error_time - time in seconds during which we are counting errors
        # Default: 10
        error_time = 10;

        # dead_time - time in seconds during which we are thinking that server is down
        # Default: 300
        dead_time = 300;

        # maxerrors - maximum number of errors that can occur during error_time to make us thinking that 
        # this upstream is dead
        # Default: 10
        maxerrors = 10;

        # protocol - protocol that is using for connecting to memcached (tcp or udp)
        # Default: udp
        protocol = tcp;
};

# bind_socket - socket credits for local bind:
# unix:/path/to/file - bind to local socket
# inet:port@host - bind to inet socket
# Default: bind_socket = unix:/var/tmp/rmilter.sock;

bind_socket = unix:/var/run/rmilter/rmilter.sock;

# tempdir - path to directory that contains temporary files
# Default: $TMPDIR

tempdir = /spool/tmp;

# max_size - maximum size of scanned mail with clamav and dcc
# Default: 0 (no limit)
max_size = 10M;

# spf_domains - path to file that contains hash of spf domains
# Default: empty

spf_domains = rambler.ru, mail.ru;

# use_dcc - whether use or not dcc system
# Default: no

use_dcc = yes;

# whitelisted recipients
# domain are whitelisted as @example.com
whitelist = postmaster, abuse;

# rule definition:
# rule {
#       accept|discard|reject|tempfail|quarantine "[message]"; <- action definition
#       [not] connect <regexp> <regexp>; <- conditions
#       helo <regexp>;
#       envfrom <regexp>;
#       envrcpt <regexp>;
#       header <regexp> <regexp>;
#       body <regexp>;
# };

# limits section
limits {
        # Whitelisted ip
        limit_whitelist_ip = 194.67.45.4;
        # Whitelisted recipients
        limit_whitelist_rcpt =  postmaster, mailer-daemon;
        # Addrs for bounce checks
        limit_bounce_addrs = postmaster, mailer-daemon, symantec_antivirus_for_smtp_gateways, <>, null, fetchmail-daemon;
        # Limit for bounce mail
        limit_bounce_to = 5:0.000277778;
        # Limit for bounce mail per one source ip
        limit_bounce_to_ip = 5:0.000277778;
        # Limit for all mail per recipient
        limit_to = 20:0.016666667;
        # Limit for all mail per one source ip
        limit_to_ip = 30:0.025;
        # Limit for all mail per one source ip and from address
        limit_to_ip_from = 100:0.033333333;
};

beanstalk {
        # List of beanstalk servers, random selected
        servers = bot01.example.com:3132;
        # Beanstalk protocol
        protocol = tcp;
        # Time to live for task in seconds
        lifetime = 172800;
        # Regexp that define for which messages we should put the whole message to beanstalk
        # now only In-Reply-To headers are checked
        id_regexp = "/^SomeID.*$/";
};

dkim {
    domain {
        key = /usr/local/etc/dkim_example.key;
        domain = "example.com";
        selector = "dkim";
    };
    domain {
        key = /usr/local/etc/dkim_test.key;
        domain = "test.com";
        selector = "dkim";
    };
    header_canon = relaxed;
    body_canon = relaxed;
    sign_alg = sha256;
    auth_only = yes;
};

NOTES

There are several things that might be useful to notice.

The order of checks:

1. DKIM test from and create signing context (MAIL FROM)
2. Ratelimit (RCPT TO)
3. Greylisting (DATA)
4. Ratelimit (EOM, set bucket value)
5. Rules (EOM)
6. SPF (EOM)
7. Message size (EOM) if failed, skip clamav, dcc and spamd checks
8. DCC (EOM)
9. Clamav (EOM)
10. Spamassassin (EOM)
11. Beanstalk (EOM)
12. DKIM add signature (EOM)

Keys used in memcached:

• rcpt - bucket for rcpt filter
• rcpt:ip - bucket for rcpt_ip filter
• rcpt:ip:from - bucket for rcpt_ip_from filter
• rcpt: - bucket for bounce_rcpt filter
• rcpt:ip: - bucket for bounce_rcpt_ip filter
• md5(from . ip . to) - key for greylisting triplet (hexed string of md5 value)

Postfix settings

There are several useful settings for postfix to work with this milter:

smtpd_milters = unix:/var/run/rmilter/rmilter.sock
milter_mail_macros =  i {mail_addr} {client_addr} {client_name}
milter_protocol = 6