NAME
asmtpd.conf - Avenger SMTP Daemon configuration file
DESCRIPTION
asmtpd.conf is the configuration file for asmtpd(8), the Mail Avenger
mail server. The file contains a series of directives, where each
directive takes zero or more arguments. Blank lines and lines
beginning with "#" (for comments) are ignored. If a line ends with the
"\" character, the "\" is ignored and the following line is appended.
In this way you can break a long list of argument over multiple
"continuation" lines.
Arguments are separated by spaces. However, you can include space in
an argument by surrounding the argument with double-quote (""")
characters. A backslash ("\") followed by any other character is
interpreted as that character. Thus, a literal """ or "\" character
can be included as "\"" or "\\", and an alternative to putting double
quotes around an argument with spaces is simply to put a "\" before
each space.
If you change asmtpd.conf while asmtpd is running, you must send it a
SIGHUP signal for it to read the new changes. (Note, however, that
asmtpd will re-read the AliasFile, DomainFile, or SPFHostsFile
automatically if you change these.)
The rest of this man page details the various directives. Directives
are case-insensitive. Depending on the directive, the arguments may or
may not be case sensitive.
GENERAL CONFIGURATION DIRECTIVES
Separator Character
This is the only option that probably needs to be set at all sites.
Character is a single character that separates usernames from the
rest of the local part of an email address. For example, with
sendmail, mail for <name+extra@host.domain> is usually delivered to
user name. Thus, a "+" should be specified for Character. With
qmail, it is <name-extra@host.domain> that belongs to user name
(though routing is handled differently). Thus, qmail users will
want to specify "-". The default is not to have a separator. This
is probably wrong for most sites, but is a lot less bad than
selecting the wrong character!
Hostname name
"Hostname" specifies the hostname that asmtpd should use in the
SMTP protocol. Ordinarily, this name should map to the IP address
of your server (or one of the IP addresses of your server). The
default is to use the local hostname (as returned by the
"gethostname" system call), with the default DNS domain name
appended if your hostname does not include any "." characters.
LogPriority priority
This directive sets the priority with which diagnostic messages are
sent to the system log. The default value is "mail.info".
LogTag tag
This directive sets the tag for syslog messages generated by
asmtpd. The default tag is empty. Note that by default most
messages except those created by Debug options already contain
"asmtpd:".
EtcDir directory
Sets the directory in which asmtpd will search for various
configuration files, including aliases, domains, and spfhosts (see
below), as well as four special rule files run under the
AvengerUser UID: default, unknown, secondary, and relay.
The file unknown consists of avenger rules that get run for any
local user that does not exist in the password file, or that exists
but has a UID of 0 (root), or that exists but has an invalid shell
(not listed in /etc/shells). These rules are not run for normal
users, even if those users do not have a .avenger directory.
The default file consists of rules that are run after the rules in
unknown or after the rules in a user’s .avenger directory, so long
as these rules did not immediately reject, defer, accept, redirect,
or bodytest the mail. If a user does not have a .avenger
directory, the rules in default are always run.
The secondary ruleset contains rules that are run if MxLocalRcpt
has been set to 1, mail is received for user@hostname, and the mail
server is an MX record for hostname, but not the highest priority
MX record. If the ruleset does not exist or simply exits, the
default is to spool the mail.
The relay ruleset consists of rules that are run when mail is
received for user@hostname where hostname is not in the domains
file (and, if MxLocalRcpt is 1, the server is not an MX record for
hostname). In such circumstances, if the sender address is local,
asmtpd will first attempt to execute an appropriate "mail" (as
opposed to the usual "rcpt") ruleset in the user’s .avenger
directory. If that ruleset does not exist or simply exits, or
hostname is not local, then asmtpd runs relay. If the rules in
relay simply exit or the file does not exist, the default is to
reject the mail.
The default value of EtcDir is /etc/avenger.
NETWORK CONFIGURATION PARAMETERS
BindAddr IP-address [port-no]
"BindAddr" specifies the IP address on which the server should
listen. The default is 0.0.0.0 (INADDR_ANY), meaning to accept
incoming connections on any IP address. By default the server uses
TCP port 25, but port-no can be also specified to chose a different
port number.
MaxClients val
Specifies the maximum number of concurrent TCP connections from
clients that asmtpd should allow. The default value is 60.
MaxConPerIP val
Specifies the maximum number of incoming TCP connections asmtpd
should accept from a single IP address. The default value is 10.
SMTPFilter prog
Specifies the name of a program asmtpd can invoke to enable packet
filtering of incoming SYN packets from a particular IP address for
the SMTP port (25 by default). Note that this program should
filter only TCP packets to the SMTP port that have the TCP SYN flag
set and the ACK flag cleared. It is very important that this rule
not interfere with previously established TCP connections, since
asmtpd uses this to block new connections when the per-IP-address
limit has been reached.
The program will be run three different ways:
prog clear
prog add IP-addr
prog del IP-addr
The clear command should cause all previously filtered IP addresses
to be re-enabled. The add command says to add the particular IP
address to the list of filtered addresses. del says to remove an
IP address from the list of addresses.
Since the details of how to filter IP packets depend entirely on
the particular operating system and firewall software being run,
this task is best handled by a shell script written by the system
administrator. An example script for use with OpenBSD’s pf packet
filter can be found in /usr/local/share/avenger/smtp-filter.pf. An
example for use with Linux’s iptables firewall can be found in
/usr/local/share/avenger/smtp-filter.iptables.
MaxMsgsPerIP msgs-per-hour [msgs-max]
Specifies the maximum rate at which asmtpd will allow successful
SMTP RCPT commands from a particular IP address. After this limit
is reached, further RCPT commands will be rejected with a temporary
SMTP error code saying too much load. msgs-per-hour is the number
of RCPT commands per hour. msgs-max is the hard limit after which
further RCPTs are refused. msgs-max, if not specified, defaults to
the same value as msgs-per-hour. However, it can be set to a
greater value to accept bursts of traffic.
MaxErrorsPerIP msgs-per-hour [msgs-max]
Similar to MaxMsgsPerIP, except this parameter specifies the
maximum rate at which clients from a particular IP address can
issue SMTP commands that return errors. If a client is issuing too
many commands that cause errors (as can often happen with spambots
that don’t check the results of commands, or that relay spam
through HTTP proxies), asmtpd will temporarily filter new
connections from that client if SMTPFilter has been specified.
Otherwise, it will immediately shutdown any incoming new TCP
connections from the client with a temporary SMTP error code.
MaxMsgsPerUser msgs-per-hour [msgs-max]
Specifies the maximum rate at which asmtpd will allow successful
SMTP RCPT commands from a particular authenticated user. The name
used for the check is either the username from SASL authentication,
or the common name of the client certificate with SSL
authentication. With this feature, you can prevent people who have
legitimate relay privileges from sending bulk mail, as might happen
if a spammer somehow stole a SASL password.
MaxRcpts val
Specifies the maximum number of recipients on a single message.
Once this number is reached, asmtpd rejects further recipients with
a temporary SMTP error code, causing the sender to send a separate
copy of the message to the remaining recipients. The default value
is 5. (Note that this limit does not apply to trusted clients.)
MaxRelayRcpts val
If val is greater than the number of recipients specified for
MaxRcpts, then this specifies a higher limit on the number of
recipients when recipients are accepted by the relay script.
MaxMsgSize bytes
The largest mail message asmtpd should accept. The default value
is 104,857,600 (100 MBytes).
SMTPTimeout seconds
Determines how long asmtpd will keep an open connection from a
client while awaiting an SMTP command.
DataTimeout seconds
Determines how long asmtpd will keep an idle connection from a
client open while waiting for mail message contents (after the SMTP
DATA command). It is advisable to set a reasonable DataTimeout
even if SMTPTimeout is short, so as not to force a client behind an
unreliable network connection to keep having to start over.
SMTPCB [0|1|2]
If set to 2 (the default), asmtpd will attempt to verify the sender
address of mail messages by going through the initial steps of
sending back a bounce message, a technique known as an "SMTP
callback." If the mail cannot get through, the SENDER_BOUNCERES
environment variable will contain an SMTP error code, and
MAIL_ERROR will be set to reject the mail by default. The next
several parameters (ClientTimeout, VrfyDelay, VrfyCacheTime, and
MaxRevClients) control the behavior of SMTP callbacks.
If SMTPCB is set to 0, SMTP callbacks are entirely disabled. If it
is set to 1, then asmtpd still performs callbacks and sets the
SENDER_BOUNCERES environment variable, but does not set MAIL_ERROR
or reject mail by default if the callback fails.
ClientTimeout seconds
Specifies the SMTP timeout for asmtpd when it acts as an SMTP
client, probing remote servers to check the validity of the sender
address on incoming mail messages. The default value is 300.
VrfyDelay seconds
When probing a remote SMTP server to validate an email address,
asmtpd will keep the TCP connection open at least this long (after
sending an HELO/EHLO command) before probing the address. The idea
is to make bulk mailing harder by preventing remote servers from
validating more than a few thousand (or a few tens of thousands of)
email addresses per second. The default value for seconds is 2.
VrfyCacheTime seconds
If asmtpd probes a remote server and discovers that it cannot send
bounce messages to an address, it caches the result for this amount
of time. If someone is mailbombing an asmtpd server from a forged
address, this option prevents asmtpd from initiating too many
connections to the forgery victim’s mail server. (Of course, if
the victim publishes an SPF record, asmtpd will never contact the
server and this is not an issue.) The default vaule for seconds is
300.
MaxRevClients val
The number of idle reverse SMTP connections (to remote SMTP
servers) to cache when not in use. These connections are used to
validate sending addresses of received mail. This number is
approximate.
IdentTimeout seconds
The number of seconds to wait for the client to respond to an
RFC1413 ident lookup. The default is 15.
SynFp [0|1]
If set to 0, disables the collection of SYN fingerprint
information, which asmtpd ordinarily includes in headers of mail
messages and in the CLIENT_SYNFP environment variable of avenger
processes. The default value is 1.
SynFpWait msec
Sets the number of milliseconds after accepting a TCP connection
that asmtpd should wait to receive the full SYN packet from the
packet filter (bpf) device. If the time is exceeded, no SYN
fingerprint will be recorded for the connection. The default value
is 500.
SynFpBuf count
Sets the maximum number of SYN fingerprints to keep around while
waiting for the corresponding connections. The default value is
100.
SynOsMTU size
Sets an additional size to try for the network’s maximum
transmission unit (MTU) when guessing the client operating system.
If size is set to 0, asmtpd will only try the value in the TCP MSS
option + 40 bytes. (Otherwise, when size is non-zero, asmtpd tries
both MSS + 40 and size.) The default for size is 1500.
NetPath [0|1]
If set to 0, disables the collection of IP "traceroute"
information, which is normally included in the headers of mail
messages and in the CLIENT_NETPATH environment variable of avenger
processes. The default value is 1.
MAIL PROCESSING DIRECTIVES
TrustedNet IP-addr/len
If the first len bits of a client’s IP address match IP-addr, the
client will be considered trusted. Trusted clients can relay mail
through asmtpd to arbitrary addresses, and do not undergo any
checks or processing by any avenger scripts. This option can be
given multiple times to list multiple networks.
TrustedDomain domain
If a client’s verified DNS name is domain or ends .domain, the
client will be considered trusted, and as described above will be
allowed to relay mail unchecked. This option can be given multiple
times to list multiple domains.
SASL [0|1|2]
This option only exists if asmtpd has been compiled with SASL
support (via the --enable-sasl option to "configure"). If set to 0
(the default), the AUTH SMTP verb is disabled, and asmtpd performs
no SASL authentication. If set to 1, asmtpd performs SASL
authentication when requested by clients, but does not inherently
trust SASL-authenticated users. You must check the AUTH_USER
environment variable in the system-wide relay script and explicitly
permit users to relay mail.
If SASL is set to 2, then clients that have authenticated via SASL
can relay mail just like TrustedNet and TrustedDomain machines--no
further scripts are run. However, the authenticated user name is
still recorded in the Received: header to track abuse, and
MaxMsgsPerUser is still enforced to prevent bulk mailing. 2 is a
reasonable value for ordinary usage, since users without permission
to relay mail have no reason to be listed in the SASL database
file.
For more information on SASL, see the SASL home page at
<http://asg.web.cmu.edu/sasl/>.
InsecureSASL [0|1]
When set to 0, which is the default, plaintext SASL authentication
is disabled unless the connection is encrypted with SSL. If set to
1, plaintext authentication is allowed even over unencrypted
connections, which is insecure.
MxLocalRcpt [0|1]
If set to 1, asmtpd will accept mail for user@host even if host
does not appear in DomainFile, as long as the local server’s IP
address corresponds to one of the DNS MX records for host.
Decisions about accepting mail will be made by the policies in the
file secondary in EtcDir.
AvengerUser username
Specifies the user in the password file whose identity asmtpd
should assume when running system-wide default rules, as well as
the mail injection program specified by Sendmail. The default
value is "avenger". Note that for efficiency, asmtpd will cache
the user and group IDs of this user. If for instance, you change
the AvengerUser’s group membership, you will have to send asmtpd a
SIGHUP signal (or restart it).
Sendmail program [arg ...]
Specifies the program to run to inject new mail messages into the
system. The default value is:
sendmail -oi -os -oee
Whatever arguments you give, asmtpd will additionally supply the
sender and recipient(s) by appending the following options:
-f sender -- recipient-1 [recipient-2 ...]
The -oee flag tells sendmail always to exit cleanly even if it
generated a bounce message. Without it, sometimes sendmail
generates a bounce for a message and exits with an error code,
which would cause asmtpd to generate an error despite the fact that
the message has already been bounced. This results in multiple
bounces for the same message.
Note that some sendmail replacements (including Exim) do not
support the -oee flag. However, these systems typically behave
correctly even without the -oee flag, meaning their sendmail
programs exit cleanly if and only if the sender no longer needs to
worry about the message. If your sendmail executable rejects the
argument -oee, try using -oem instead.
EmptySender sender
In some old versions of sendmail, running
sendmail -f ''
(where ’’ is a zero-length argument) does not produce an empty
envelope sender, as should happen for bounces. EmptySender lets
you specify an alternate sender to use for the empty envelope
sender. Try using the single-character string "@"--that seems to
produce the desired envelope sender (which turns into MAILER-
DAEMON) with both old and new versions of sendmail, though it is
not necessarily compatible with other MTAs.
SendmailPriv [0|1]
By default, asmtpd drops privilege to run Sendmail as AvengerUser.
If, however, you specify SendmailPriv 1, asmtpd will instead run
Sendmail as root. One possible use of this, for users of the
sendmail MTA, is to invoke sendmail with the -Am flag, which
requires root privileges but bypasses an extra level of queuing.
(Note that with newer versions of sendmail, if you do not run
sendmail as a daemon on address 127.0.0.1, you will have to
configure asmtpd to use the -Am flag.)
SendmailFromLine [0|1]
If you set this value to 1, the message fed to the Sendmail program
will start with a UNIX mailbox style "From " line (which is not
actually part of the message header). The default value is 0.
AliasFile path
Specifies the path of the user-mapping file, which by default is
the file aliases in the directory specified by EtcDir. Each line
of this file is of the form:
prefix: replacement
Before deciding which user’s rules to process for a particular mail
message, the local part of the email address is transformed based
on the aliases file. An address of prefix is replaced by the
replacement. In addition, if the Separator character has been
defined, then if an address begins with prefix followed immediately
by the separator character, replacement is also substituted. If
the alias file contains multiple matching prefixes, the longest one
is chosen. Alias substitution continues recursively unless a loop
is detected or the recursion reaches a depth of 20.
Note: It is important to emphasize that the aliases mechanism only
governs which user checks the validity of a particular piece of
mail. It does not affect where the mail is eventually delivered,
should the resulting rules accept the mail.
DomainFile path
Specifies the path of the domain-mapping file, which by default is
the file domains in the directory specified by EtcDir. This file
allows one to map responsibility for all users in a domain onto a
particular local user. Each line of the file must have one of the
following forms:
domain:
domain: user
domain: userSEPARATOR
In the first case, when receiving mail for local@domain, the local
part local is simply taken as is and treated as a local username
(with the first separator character and anything following
removed). In the second case, the mail is checked by user instead.
In the third case, SEPARATOR is the separator character, which must
have been declared with a Separator directive. Here, user and the
separator character are pre-pended to local. For instance, if
SEPARATOR is -, the mail would be checked by user-local. In all
cases, the result of the mapping is subject to alias substitution
as described for AliasFile.
Note: As with AliasFile, the domain mechanism only governs which
user checks the validity of a particular piece of mail. It does
not affect where the mail is eventually delivered, should the
resulting rules accept the mail.
Env var[=value]
Specifies an environment variable to supply when running avenger.
Ordinarily, avenger is run with a clean environment, with only a
few variables such as PATH passed through. If the Env directive
specifies a value, the environment variable will be be set to this
value. If =value is omitted, asmtpd will pass through the value of
the environment variable it inherits, or leave the variable unset
if it is not set in the environment in which asmtpd is run.
AvengerMaxPerUser val
Specifies how many concurrent avenger processes to launch for a
particular user. If a particular user already has this many
avenger processes running, and another SMTP client issues an RCPT
command that resolves to the same local user (or another local user
with the same numeric UID), then asmtpd will wait for one of the
existing avenger processes to exit before launching a new avenger
to evaluate the new RCPT command. The default for val is 5. This
limit does not apply to the system-wide unknown, default, and relay
files processed under the AvengerUser UID. (Note that bodytests
run for a particular user are also included in that user’s count of
avenger processes.)
AvengerTimeout seconds
Specifies a timeout value after which asmtpd will attempt to kill
an avenger process, in case the process has somehow gotten stuck.
asmtpd does this, before launching avenger, by setting an alarm for
the process. The default for seconds is 600.
NoCheck user[<@>host]
Specifies that asmtpd’s internal checks for email validity should
be bypassed for email to a particular email address. If host is
not specified, then this applies to user at any acceptable local
host (asmtpd still will not allow relaying, of course). It is a
good idea to enable this for usernames specified in RFC 2142, such
as postmaster and abuse.
RBL [-i] [-p] [-f] -s score domain
Checks real-time blackhole list domain. If -i is present, looks up
the client’s IP address reversed (i.e., for client 1.2.3.4, this
will match when DNS name 4.3.2.1.domain exists). If -p is present,
the name of the client (as specified by a verified PTR DNS record)
will be looked up. If -f is present, the hostname from the
envelope sender (the address in the SMTP MAIL) command will be
looked up (i.e., mail from user@host matches if host.domain
exists). If none of -i, -p, or -f is specified, -i is assumed by
default.
score is an integer (which can be negative). The scores of all
matching RBLs are added together, and a message is rejected if the
total is greater than or equal to 100.
UserMail [0|1]
If set to 0, asmtpd will not chack mail* files in users’ .avenger
directories, but will always use the system-wide relay file (and
secondary file) to decide whether to relay mail. The default value
is 0.
UserRcpt [0|1]
If set to 0, asmtpd will not chack rcpt* files in users’ .avenger
directories, but will always use the system-wide default file. The
default value is 1.
AllowPercent [0|1]
If set to 0 (the default), asmtpd will reject any email whose local
part contains a "%" character. This is because many MTAs will
relay mail for users of the form user%host1@host2 to user@host1.
While of course it is possible to reject such messages with the
/etc/avenger/unknown file, it is easy to forget to do so. Failing
to do so can get your site listed in various spam source lists,
which will have some serious consequences. For that reason,
AllowPercent is 0 by default. Set it to 1 if you really do want
mail for users with "%" characters.
AllowDNSFail [0|1|2]
Upon accepting a connection from a client, asmtpd attempts to
resolve the client’s IP address to a hostname. If a temporary DNS
error occurs and AllowDNSFail is set to 0 (the default), asmtpd
will reject the connection immediately. If AllowDNSFail is set to
1, however, then asmtpd will accept the connection and continue.
However, in this case that the CLIENT_DNSFAIL environment variable
will be set to an error message, and mail will still be rejected by
default unless an rcpt script explicitly calls accept. If
AllowDNSFail is set to 2, then CLIENT_DNSFAIL will still be set,
but by default mail will be accepted unless explicitly rejected.
Note that this option has no effect on IP addresses that don’t
resolve to a domain name (e.g., where a lookup of the in-addr.arpa
domain returns an empty result or the NXDOMAIN error).
SSL CONFIGURATION PARAMETERS
SSL [0|1|2]
This and the following options are supported if Mail Avenger has
been compiled with support for the STARTTLS command (using the
--enable-ssl option to "configure"). If SSL is set to 0, then the
STARTTLS command will be disabled.
If SSL is set to 1 (the default), then STARTTLS will be enabled
profiled the private key and certificate files can be found.
(Since these files will not exist by default, STARTTLS is still
disabled by default.) Relaying based on client certificates can be
enabled by checking the SSL_ISSUER and SSL_SUBJECT environment
variables in the relay script.
If SSL is set to 2, then authentication with any valid client
certificate will allow mail relaying with no further checks. This
value makes sense only if your organization runs a private
certificate authority and you only place your local CA key in the
SSLCAcert file, as otherwise you will have no control over who can
relay mail through your machine.
SSLCAcert path
SSLCAcert specifies the certificate authorities allowed to sign
client certificates. path must be a file containing one or more
trusted CA certificates in PEM format. If <path> is not an
absolute path name, asmtpd will look for the file in EtcDir. The
default path is cacert.pem.
SSLCRL path
If SSL is in use, path specifies a PEM-format certificate
revocation list. The default value is crl.pem.
SSLkey path
If SSL is in use, path specifies a PEM-format file containing the
server’s private key. If the file is not present, the STARTTLS
command will be disabled. The default path is privkey.pem.
SSLcert path
If SSL is in use, path specifies a PEM-format file containing a
certificate for the public key corresponding to private key SSLkey.
If the file is not present, the STARTTLS command will be disabled.
The default path is cert.pem.
SSLciphers string
string specifies the preference for ciphers with SSL. For example,
to allow all ciphers except anonymous Diffie-Hellman, low key
sizes, exportable ciphers, and MD%-based MAC, and to sort ciphers
by strength, you might use the following string>:
ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH
By default, asmtpd just uses the OpenSSL library’s default cipher
preferences.
SPF CONFIGURATION PARAMETERS
SPFfail [SPF-rule ...]
SPF (Sender Policy Framework) is a mechanism to prevent forgery of
email sender addresses. (More information is available at
<http://www.openspf.org/> and in the forthcoming RFC 4408.) asmtpd
always runs SPF checks on incoming email. An SPF check returns one
of seven possible results: none, neutral, pass, fail, softfail,
error, or unknown. asmtpd will reject mail if the result is fail
(and defer mail if the result is error).
The SPFfail directive provides a second chance to mail that would
otherwise resolve to fail. If SPF rules are provided with this
directive, and the SPF check on a message resolves to fail, then
asmtpd will re-evaluate the message with the rules from the SPFfail
directive. If the SPFfail rules evaluate to none, neutral, or
unknown, then the original fail result will remain. Otherwise, the
result of the SPFfail rules overrides the fail result.
This directive can be used to work-around the problem of sites,
such as evite.com, that forge email, but do not actually send spam.
trusted-forwarder.org maintains a white-list of such sites, and it
is highly recommended that you use this whitelist until SPF is more
widely deployed. To do so, you can use the configuration line:
SPFfail include:spf.trusted-forwarder.org
SPFnone [SPF-rule ...]
This directive is similar to SPFfail, but supplies additional SPF
rules to be run in the event that the SPF result for a message
resolves to none--meaning that the domain from which the mail comes
does not publish an SPF record. One possible use might be the
following:
SPFnone a/24 mx/24 ptr
This rule says that if the sending domain does not publish an SPF
record, consider its result to be pass nonetheless as long as the
sending host shares a 24-bit IP prefix with the address of the
domain, or the address of any of the mail exchangers (DNS MX
records) for the domain, or if the domain name of the sending
machine has the sender domain name as a suffix.
SPFlocal [SPF-rule ...]
Unlike the previous two rules, which provide hooks to run after an
SPF result has been determined, SPFlocal supplies SPF rules to be
run before even attempting SPF rules for the domain. If the local
rules return pass, fail, softfail, or error, this reult becomes the
SPF result for the message. Otherwise, asmtpd evaluates the
appropriate rules for the domain as usual.
An example use might be to reject mail from a real-time black hole
list (RBL), such as spamcop:
SPFlocal -exists:%{ir}.bl.spamcop.net
SPFexp [explanation ...]
Provides a default explanation for an SPF failure, if the sender
domain does not have one. The default is:
SPFexp See http://www.openspf.org/why.html?sender=%{S}&ip=%{I}
SPFHostsFile path
This specifies the pathname of a file that contains "fallback" SPF
records for domains that fail to supply SPF records themselves.
This file effectively achieves the same result as SPFNone, but on a
per-hostname basis. The default path is spfhosts in the directory
specified by EtcDir (or /etc/avenger by default). Each line of the
file has the form:
domain: SPF-rules
domain is the domain name for which the SPF-rules apply. If domain
starts with a ".", then the rule matches all host names with domain
as a suffix. In other words, ".yahoo.com" matches
"mail.yahoo.com", "mx.yahoo.com", but not "yahoo.com". Note that
if a domain publishes an SPF record through DNS, the record in DNS
overrides the record specified in this file.
As an example, suppose Microsoft does not publish an SPF record in
DNS, but you happen to know that all mail from users at
"microsoft.com" comes from machines whose reverse DNS mapping ends
either "microsoft.com" or "msft.com", or else whose IP addresses
share a 16-bit prefix with one of the mail exchangers for
"microsoft.com". You might place the following line in your
spfhosts file:
microsoft.com: ptr ptr:msft.com mx/16 ~all
Here "~all" resorts to softfail when the sender does not match,
which tags the message but does not reject it. Use "-all" to
reject the mail outright. Note that if Microsoft ever starts
publishing an SPF record in DNS, it will override the above line.
DEBUG PARAMETERS
DebugSMTP [0|1]
When set to 1, causes asmtpd to log a complete trace of all SMTP
traffic to and from connecting clients. Produces a large amount of
data, but can be useful for debugging. Each trace line list the
name of the connecting client and asmtpd’s file descriptor number
in parentheses.
DebugSMTPc [0|1]
When receiving mail, asmtpd connects to remote mail servers to
ensure the envelope sender addresses of incoming messages are valid
email addresses, and in particular that they can receive bounces.
When DebugSMTPc is set to 1, all outgoing SMTP connection traffic
from SMTPc is logged. The output format is similar to DebugSMTP,
but file descriptor numbers are prefixed with "R" to indicate this
is a reverse connection.
DebugAvenger [0|1]
Prints a trace of input and output to all avenger processes run.
The name also has a file descriptor number prefixed with "a" for
avenger.
FILES
/etc/avenger/asmtpd.conf
default location of file
/etc/avenger
default for EtcDir, location of other configuration files
aliases, domains, spfhosts
see the descriptions of AliasFile, DomainFile, and SPFHostsFile
above
unknown, default, secondary, relay
avenger rules to be run by the AvengerUser under different
circumstances; see the description of EtcDir above, and the manual
page for avenger(1)
/var/run/asmtpd.pid
File containing the process ID of a running asmtpd process. You
must send this process a SIGHUP signal for it to re-read the
asmtpd.conf file.
/usr/local/share/avenger/asmtpd.conf
/usr/local/share/avenger/unknown
Example configuration files.
/usr/local/share/avenger/smtp-filter.pf
/usr/local/share/avenger/smtp-filter.iptables
Example scripts for the SMTPFilter directive.
SEE ALSO
asmtpd(8), avenger(1)
The Mail Avenger home page: <http://www.mailavenger.org/>.
AUTHOR
David Mazieres