smtpserver - zmailer SMTP server
smtpserver [ -46aBigntVvw ] [ -p port ] [ -l SYSLOG ] [ -l logfile ] [ -s[ftveR] ] [ -s strict ] [ -I pidfile ] [ -L maxloadaver ] [ -M SMTPmaxsize ] [ -P postoffice ] [ -R router ] [ -C cfgfile ] [ -T '[1.2.3.4]' ]
This program implements the server side of the SMTP protocol as described in RFC821, and knows about the common extensions to the protocol expected by Sendmail and BSMTP clients.
By default the program will kill the previous smtpserver daemon, if any, then detach and listen for SMTP connections. Incoming messages will be submitted for processing using the zmailer(3) interface to ZMailer. Nontrivial address checking is done asynchronously, although this behaviour can be changed by a command line option if you cannot afford to transfer data just to bounce it back. All checking is done by executing the router(8) program in interactive mode, and executing a wellknown shell function with wellknown parameters for each request.
-4 |
Explicitely to use IPv4 type of socket even on machines that is capable to do IPv6 type of sockets. |
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-6 |
Explicitely to (try to) use IPv6 type of socket even if the machine does not support it. For a default the server will try to use IPv6, if it has been compiled on an environment where it is present, but will do a fallback to IPv4 in case the runtime system does not have IPv6. |
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-a |
turn on RFC931/RFC1413 indentification protocol, and log the information acquired with it to the submitted file. |
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-w |
turn on usage of "whoson" protocol. This option is available even if actual code is not available. |
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-g |
the gullible option will make the program believe any information it is told (such as origin of a connection) without checking. |
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-i |
runs the server interactively, which makes it usable for processing a batched SMTP stream (BSMTP) on stdin. With -v option this echoes incoming BSMTP to create more accurate faximille of BITNET BSMTP mailers. |
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-l SYSLOG |
A magic value of "SYSLOG" for the logfile is interpreted by directing all session log stuff thru syslogd; something which may require better syslogd, than your system has by default; see ``syslogng'' at a well indexed free software sites. |
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-l logfile |
specifies a logfile and enables recording of incoming SMTP conversations. If you want both file based session log, and syslog() based, issue this option after ``-l SYSLOG'' one. |
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-n -p -B |
indicates the program is being run from inetd(8). specifies the TCP port to listen on instead of the default SMTP port, 25. flags the email to arrive via BSMTP channel (via BITNET, for example). |
-I pidfile -L maxloadaver |
specifies an alternate PID file location. tells the maximum loadaverage the system is under when we still accept email in. |
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-M SMTPmaxsize |
Defines the asolute maximum size we accept from incoming email. (Default: infinite) (This is local policy issue.) |
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-P postoffice -R router -C cfgfile |
specifies an alternate POSTOFFICE directory. specifies an alternate router (8) program to use for address verification. specifies nonstandard configuration file location; the default is $MAILSHARE/smtpserver.conf. |
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-s strict |
this turns on all kinds of strict smtp protocol adherence checks, which in normal life can be relaxed slightly. Great for compliance testing ;) |
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-s [ftveRS] |
specifies the style of address verification to be performed. There are four independent commands that can invoke some kind of address verification, and four independent flags to control whether this should be done. They are: |
The flags are concatenated to form the argument to the -s option. The |
default is ve. |
-T '[1.2.3.4]'
-T '[ipv6.hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:1.2.3.4]'
Supply (in interactive mode) test address for policy dataset address |
testing. The optionset recommended for that case is: |
-i -d 1 -T '[1.2.3.4]' |
A notable detail is that to see what really is going on in the policy analysis, one must usei the ``d 1'' option to turn on the debugging early enough to see its initial verdict at the time the ``220..'' greeting banner is produced.. Also notable is that brackets in the supplied IP address must be present, otherwise illegal syntax will be reported. (Using RFC 821 address literal parser here.) |
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-t |
Set when running smtpserver under e.g. inetd, and using service port number 465; a "wellknown" deprecated one of SSL/SMTP; (From the era before ``STARTTLS'' protocol verb.) |
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-V |
prints a version message and exits. |
If the $MAILSHARE/smtpserver.conf exists it is read to configure two kinds of things:
PARAM -entries |
allow server starttime parametrization of several things, including: |
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The style (-s) option |
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behaviour based on glob patterns matching the HELO/EHLO name given by a remote client. Lines beginning with a # or whitespace are ignored in the file, and all other lines must consist of two tokens: a shellstyle (glob) pattern starting at the beginning of the line, whitespace, and a sequence of style flags. The first matching line is used. As a special case, the flags section may start with a ! character in which case the remainder of the line is a failure comment message to print at the client. This configuration capability is intended as a way to control misbehaving client software or mailers. |
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PARAM maxsize |
This is synonym to starttime -M option. |
PARAM min-availspace 5000
This defines, in kilobytes, the minimum available space in |
PARAM max-error-recipients
This defines how many recipients can be on a message whose source address is MAIL FROM:<>. That is, is an error message. (Sometimes SPAMs are tried to inject in that form...) |
PARAM MaxSameIpSource
This sets the maximum number of active connections from any given single IP address. When the limit is reached, system tells the remote end: ``450 Too many simultaneous connections...'' (and then closes the connection.) When the limit is exceeded by factor of four, the server just closes the connection without telling anything. Do note that this works only when the smtpserver is running as its own daemon, not while run from under inetd! |
PARAM MaxParallelConnections
This limits how many simultaneous connections the server will accept in total e.g. how many childs a master server can have running. Default value: 800. Exceeding the limit by less than 100 will get a message ``450 Too many simultaneous connections...'' printed to the connection. In every case the connection is closed right after the possible message. Do note that this works only when the smtpserver is running as its own daemon, not while run from under inetd! |
PARAM ListenQueueSize
This sets the listen queue size parameter for listen(2) call at the server. PARAM TcpRcvBufferSize
This sets setsockopt(SO_RCVBUF) value, in case the system default is not suitable. |
PARAM TcpXmitBufferSize
This sets setsockopt(SO_SNDBUF) value, in case the system default is not suitable. |
PARAM RcptLimitCount 10000
This sets the maximum number of accepted recipients per one message transaction. Default (and minimum!) value is 100, which is mandated by the RFC 821. |
PARAM BindPort 25
PARAM BindAddress [0.0.0.0]
PARAM BindAddress [IPv6.0::0]
PARAM BindAddress iface:ifacename
Per default the server mode SMTPserver binds to port 25 and any locally accepted address, but occasionally people seem to want to have separate server instances with different configurations, and for those cases are these parameters. |
PARAM DEBUGcmd
PARAM EXPNcmd
PARAM VRFYcmd
This trio (DEBUGcmd, EXPNcmd, VRFYcmd) are enablers of like named SMTP verbs which have some uses in the debug mode. They are normally disabled, but running them enabled does not allow direct attacks with them. (That we know of.) |
PARAM enable-router
This enables interactive router use where user inputs reach the router. As things turn out, while the canned scripts should be safe against any and all inputs, a careless change in the router scripts may endanger this status. Per default this is disabled to protect your system. To enable EXPN and VRFY, this must be enabled, but be very carefull when you do this. This is also required for interactive router processing of ``MAIL FROM'' and ``RCPT TO'' addresses. |
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PARAM smtp-auth |
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This enables 'SMTP AUTH' facility (AUTH verb, plus optional parameter to MAIL verb). With this the users who are able to 'login' successfully to this host, are then able to relay the email thru the server unlimited. |
PARAM AUTH-LOGIN-also-without-TLS
This enables 'SMTP AUTH' facility usage also without running under SSL/TLS security envelope. |
PARAM MSA-mode
Enable Message Submission Agent mode, where smtpserver requires successful user authentication during SMTP sessions initiated from outside of the trusted networks or the networks with relaying enabled (see "fulltrustnet" and "relaycustnet" at the sample proto/db/smtp-policy.src file). |
PARAM SMTP-auth-pipe /path/to/program
This is a path to the external authentication program. The authenticator should read a username from command line and a password from standard input. Exit status 0 means successful authentication. It is relatively easy to make a mistake in external authentication program that follows the specification. Use this option only if you know exactly what you do! BE CAREFULL! |
PARAM No8BITMIME
PARAM NoCHUNKING
PARAM NoDSN
PARAM NoEHLO
PARAM NoENCHANCEDSTATUS(CODES)
PARAM NoETRN
PARAM NoPIPELINING
This set are disablers of like named Extended SMTP EHLO responses, plus EHLO verb itself, e.g. using these will turn off given (for example ``PIPELINING'') response from the EHLO replies, and then a client possibly capable to feed PIPELINING will not do it unless it breaks rules, and does it even when the server does not report facility being available. If you want to disable any of these, you better have a good reason for it, as in general they work quite fine. Of these, 8BITMIME can not in reality be disabled, only its adverticement can be turned off. |
PARAM no-multiline-replies
Turn off ZMailer's default multiline replies; many systems (especially from M$ breed) don't do RFC 821 Appendix E properly... |
PARAM policydb |
This defines smtp input policy filtering/analysis database location. See the comments at the sample proto/db/smtp-policy.src file. An error here will be reported with obscureish code; "1" = "DBTYPE parameter unknown/unsupported", "2" = "can't open the database". |
PARAM contentfilter $MAILBIN/smtpcontentfilter
An external program for received message content analysis. |
The interface to the program is simple synchronous halfduplex one, smtpserver writes relative filepath of the message into programs stdin, ending it with a newline. The filter programs reply must begin with a signed integer, then whatever text is desired to give to the user. |
PARAM tarpit n1 n2 |
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This defines a prereply slowdown factor, and next delay multiplier (both are integers). Default values are (0, 0). Delay tops at 250 (seconds). The ``n1'' is used as the initial tarpit delay, and ``n2'' is multiplier for formula: next = prev + (prev * n2) |
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PARAM rcvd-ident |
PARAM rcvd-whoson
PARAM rcvd-auth-user
PARAM rcvd-tls-mode
PARAM rcvd-tls-peer
This quintet controls what possibly collected data is shown at the |
published ``Received:'' header that this system generates. |
PARAM etrn-cluster node-name-or-address mq2-username mq2-passwd
In loadbalance clusters a network level loadbalancer may distribute the incoming SMTP connections to multiple real machines, and by using this parameter (repeatedly) to list those peers, system can relay user initiated ETRN requests to all cluster nodes. This method requires that the scheduler runs its mailq service in MAILQv2 mode! |
PARAM lmtp-mode
When desiring to test LMTP (RFC 2033), this parameter can be turned on, however ZMailer is no real LMTP server, and this feature is only for debug purposes. |
Here is a possible configuration file:
# |
# smtpserver.conf autogenerated edition |
# |
PARAM VRFYcmd
PARAM enablerouter
PARAM help Our businesshours are MonFri: 08001700 (TZ: 0700)
PARAM help
PARAM help Questions regarding our email service should be sent
PARAM help via email to address <postmaster@OURDOMAIN>
PARAM help Reports about abuse are to be sent to: <abuse@OURDOMAIN>
PARAM help
#
# Uncomment following for not to strip incoming addresses of
# form: <@aa,@bb:cc@dd> into nonsourcerouted base form: <cc@dd>
#
#PARAM allowsourceroute
#
# The policy database:
# (NOTE: See `makedb' for its default suffixes!)
# |
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PARAM policydb |
$DBTYPE $MAILVAR/db/smtp-policy |
#PARAM tarpit 0 0 # |
# No "tarpit" for 4XX/5XX reply codes |
# |
# |
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##PARAM listenssmtp |
# A deprecated TCP/465 port listener for SSL/SMTP $MAILVAR/db/smtpserverCAcert.pem |
#PARAM tlsloglevel |
0 |
# Elements to be added into "Received:" header's
# initial comment part: |
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#PARAM rcvdident |
# The ident lookup result |
# A loadbalanced server cluster may want to communicate
# the ETRN request to cluster components, here is how:
# See also: doc/guides/etrncluster
#
#PARAM etrncluster localhost mq2username mq2passwd
#PARAM etrncluster node2nameoraddress mq2username mq2passwd
#PARAM etrncluster node3nameoraddress mq2username mq2passwd
#...
#PARAM etrncluster node40nameoraddress mq2username mq2passwd
# |
The contentfilter program is started without parameters running userid of daemon in
directory $POSTOFFICE.
The program must silently wait for input, which is full path to the message spool file, analyze
it, and reply with exactly one line matching rule of: "%i " begin with signed integer, then
have one or more whitespace, then whatever filter writer liked.
General rule:
1 negatives are condemned into rejection |
0 zero is ok! gladly accepted |
1 positives are sent into the freezer |
The program may produce also the numeric SMTP reply codes in its response text:
1 |
1 250 2.7.1 Glad to see some spam, immediately destroyed :) |
0 |
0 250 2.6.0 Message OK! |
1 |
If the message has no text, some defaults are supplied. If the message text starts with
numbers, it is presumed that it contains both the SMTP reply code, and
ENHANCEDSTATUSCODE before the text. (If no ENHANCEDSTATUSCODE part is
present, then some possibly senseless default is supplied.)
Interface message text lines beginning with anything except signed integer are logged, and
the communication channel from the smtpserver to the contentfilter program is closed.
Interface continues to scan things reported by the contentfilter program, and if no properly
formatted line appears, default is to send the message into the freezer ("1");
If the ZMailer system is configured with tcpwrapper code, and ``PARAM
use-tcp-wrapper'' is active in configuration, then serviceid "smtpreceiver" is looked
for all those addresses that are allowed to feed SMTP email in.
Usually this mode of operation is not used, and files hosts.allow, and hosts.deny contain
following kind of entries:
/ETC/hosts.allow |
mailq : ALL@1.2.3.0 |
smtp-receiver: ALL@ALL |
/ETC/hosts.deny |
ALL : ALL@ALL |
Alternatively, all the functions which tcpwrapper could supply are also available thru the
policy database machinery.
(Do note that scheduler(8) has also tcp-wrapper support, which becomes active simultaneously with smtpserver's tcp-wrapper code!)
If the system has <security/pam_appl.h> file, following file will also be needed for the system:
/etc/pam.d/smtpauthlogin
#%PAM1.0
auth |
required /lib/security/pam_pwdb.so shadow |
This subsystem of smtpserver does control acceptability of recipient envelope addresses per several criteria:
smtp-policy.mx |
problems when two domainsuffixes have same ending suffix (or are the same).. (Name/keyspace problem) We can set the internal "always_accept" flag at the source IP test, and never after. |
smtp-policy.mx.manual
Who really are our MX clients. |
smtp-policy.spam |
Use this when you really know them, and don't want just to trust that if recipient has MX to you, it would be ok... You can substitute this knowledge with a fuzzy feeling by using 'acceptifmx +' attribute at the generic boilerplate. List here domain names. You CAN also list here all POSTMASTER addresses you accept email routed to: postmaster@local.domain these are magic addresses that email is accepted to, even when everything else is blocked. |
smtp-policy.spam.manual
Those users & domains that are absolutely nono for the senders, or the recipients, no matter what earlier analysis has shown. (Except for those that we absolutely trust..) |
Short usage instructions:
1. |
You can start rejecting at the connection setup and then at MAIL FROM (and RCPT TO). However many (especially M$ environment) SMTP clients won't react on that properly, and will just keep repeating the delivery attempts. |
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2. |
You can delay the rejections until RCPT addresses are given. |
Like mentioned above, this method has a problem with many clients who don't believe that
HELO can give 500series response.
Method is as follows:
Pick your choice of databases to the second variant ``_rbl0'' label by joining your selection
from various things exemplified here below by using ``:'' character as glue in between:
``+'' alias ``rbl.maps.vix.com'' |
``relays.mailabuse.org'' |
``dul.maps.vix.com'' |
``relays.orbs.org'' |
``ok.orbs.org:relays.orbs.org'' < THIS IS A PAIR! |
For the ``ok.orbs.org:relays.orbs.org'' the ZMailer 2.99.52patch2 has special
support, but it isn't entirely foolproof thing... (Due to false OKs in the OK zone while
NETBLOCK type things exist at the RELAYS zone.)
An example for the resulting attribute pair: (RBL+DUL+RSS)
#| Second RBL variant: Early block with RBL+DUL+RSS |
_rbl0 |
testdnsrbl +:dul.maps.vix.com:relays.mailabuse.org |
Delay the rejection report to ``RCPT TO'' verbs by using the ``Third RBL variant'':
#| Third RBL variant: Late block with RBL+DUL+RSS |
_rbl0 rcptdnsrbl |
The sample boilerplace will use these as defaults unless you choose to explicitely have
``testrcptdnsrbl '' at some of the recipient domains you list at smtp-policy.mx
file:
#sample.domain.with.rbl |
/etc/zmailer.conf |
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/etc/pam.d/smtpauthlogin (if PAM mechanism is present and |
plainpassword |
router(8)
RFC 1426/1652 |
ESMTP 8BITMIME |
This program authored and copyright by:
Rayan Zachariassen (was at U of Toronto)
Extended SMTP, policy facilities, etc. by
Matti Aarnio <mea@nic.funet.fi>