... I think. Problem is I am not equipped to figure out if or how.

fc6, cyrus IMAP, firewalled. I have a pop3 server on a separate machine which I use for fetch from ISP and send. The IMAP server uses fetchmail to collect from that, on a cron job.

What that means is for the majority of smtp I don't use postfix at all - only for alerts, logwatch &c.

My router NATs a small number of ports to the IMAP server.

Problem is,
(i) Logwatch shows postfix is sending a regular 300 mails a day approx - *way* more than I would expect, but perhaps is correct.

(ii) I am also getting lots of mail from people i have never heard of saying undeliverable, out of office, virus-ridden, and so on. This might be spoofing though.

So. Can anyone point me in the right direction please ? It would be irresponsible of me to ignore my doubts.

Thanks, all.
H

Post your /etc/postfix/main.cf

As far as (ii) goes, this is pretty much what you should expect when you have your own domain name - before I stopped monitoring it, I got over 500 "undeliverable mails" a day courtesy of spammers spoofing their "from" address, so I wouldn't worry about that.

(i) is more of a worry, tho..

I dunno...

I rarely get "undeliverables" to my domain names. Of course, I don't do garbage collection; an email that comes to a nonexistent mailbox gets dropped, so it could be that these undeliverables just don't get collected.

(i) is certainly a worry, motivating immediate action, IMNSHO.

Postfix is generally pretty secure out of the box. What is the setting for mynetworks (or better yet, post the output of postconf -n)

If I recall correctly. fetchmail uses POP, so you shouldn't need to allow external boxes to connect in on port 25 (SMTP) anyway. You will still need to allow outbound connections to send mail though. Try looking at your firewall settings

Wow ! Thanks for the response. I rather thought I would get 'RTFM'.



#
#relayhost = $mydomain
#relayhost = [gateway.my.domain]
#relayhost = [mailserver.isp.tld]
#relayhost = uucphost
#relayhost = [an.ip.add.ress]
relayhost = slave.37chapellane.co.uk


#
#relay_recipient_maps = hash:/etc/postfix/relay_recipients


#
#in_flow_delay = 1s


#
#alias_maps = dbm:/etc/aliases
alias_maps = hash:/etc/aliases
#alias_maps = hash:/etc/aliases, nis:mail.aliases
#alias_maps = netinfo:/aliases

#
#
#alias_database = dbm:/etc/aliases
#alias_database = dbm:/etc/mail/aliases
alias_database = hash:/etc/aliases
#alias_database = hash:/etc/aliases, hash:/opt/majordomo/aliases


#
#recipient_delimiter = +


#
#home_mailbox = Mailbox
#home_mailbox = Maildir/

# The mail_spool_directory parameter specifies the directory where
# UNIX-style mailboxes are kept. The default setting depends on the
# system type.
#
#mail_spool_directory = /var/mail
#mail_spool_directory = /var/spool/mail

# The mailbox_command parameter specifies the optional external
# command to use instead of mailbox delivery. The command is run as
# the recipient with proper HOME, SHELL and LOGNAME environment settings.
# Exception: delivery for root is done as $default_user.
#
# Other environment variables of interest: USER (recipient username),
# EXTENSION (address extension), DOMAIN (domain part of address),
# and LOCAL (the address localpart).
#
# Unlike other Postfix configuration parameters, the mailbox_command
# parameter is not subjected to $parameter substitutions. This is to
# make it easier to specify shell syntax (see example below).
#
# Avoid shell meta characters because they will force Postfix to run
# an expensive shell process. Procmail alone is expensive enough.
#
# IF YOU USE THIS TO DELIVER MAIL SYSTEM-WIDE, YOU MUST SET UP AN
# ALIAS THAT FORWARDS MAIL FOR ROOT TO A REAL USER.
#
#mailbox_command = /some/where/procmail
#mailbox_command = /some/where/procmail -a "$EXTENSION"

# The mailbox_transport specifies the optional transport in master.cf
# to use after processing aliases and .forward files. This parameter
# has precedence over the mailbox_command, fallback_transport and
# luser_relay parameters.
#
# Specify a string of the form transport:nexthop, where transport is
# the name of a mail delivery transport defined in master.cf. The
# :nexthop part is optional. For more details see the sample transport
# configuration file.
#
# NOTE: if you use this feature for accounts not in the UNIX password
# file, then you must update the "local_recipient_maps" setting in
# the main.cf file, otherwise the SMTP server will reject mail for
# non-UNIX accounts with "User unknown in local recipient table".
#
mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp

# If using the cyrus-imapd IMAP server deliver local mail to the IMAP
# server using LMTP (Local Mail Transport Protocol), this is prefered
# over the older cyrus deliver program by setting the
# mailbox_transport as below:
#
# mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp
#
# The efficiency of LMTP delivery for cyrus-imapd can be enhanced via
# these settings.
#
# local_destination_recipient_limit = 300
# local_destination_concurrency_limit = 5
#
# Of course you should adjust these settings as appropriate for the
# capacity of the hardware you are using. The recipient limit setting
# can be used to take advantage of the single instance message store
# capability of Cyrus. The concurrency limit can be used to control
# how many simultaneous LMTP sessions will be permitted to the Cyrus
# message store.
#
# To use the old cyrus deliver program you have to set:
#mailbox_transport = cyrus

# The fallback_transport specifies the optional transport in master.cf
# to use for recipients that are not found in the UNIX passwd database.
# This parameter has precedence over the luser_relay parameter.
#
# Specify a string of the form transport:nexthop, where transport is
# the name of a mail delivery transport defined in master.cf. The
# :nexthop part is optional. For more details see the sample transport
# configuration file.
#
# NOTE: if you use this feature for accounts not in the UNIX password
# file, then you must update the "local_recipient_maps" setting in
# the main.cf file, otherwise the SMTP server will reject mail for
# non-UNIX accounts with "User unknown in local recipient table".
#
#fallback_transport = lmtp:unix:/var/lib/imap/socket/lmtp
#fallback_transport =

# The luser_relay parameter specifies an optional destination address
# for unknown recipients. By default, mail for unknown@$mydestination,
# unknown@[$inet_interfaces] or unknown@[$proxy_interfaces] is returned
# as undeliverable.
#
# The following expansions are done on luser_relay: $user (recipient
# username), $shell (recipient shell), $home (recipient home directory),
# $recipient (full recipient address), $extension (recipient address
# extension), $domain (recipient domain), $local (entire recipient
# localpart), $recipient_delimiter. Specify ${name?value} or
# ${name:value} to expand value only when $name does (does not) exist.
#
# luser_relay works only for the default Postfix local delivery agent.
#
# NOTE: if you use this feature for accounts not in the UNIX password
# file, then you must specify "local_recipient_maps =" (i.e. empty) in
# the main.cf file, otherwise the SMTP server will reject mail for
# non-UNIX accounts with "User unknown in local recipient table".
#
#luser_relay = $user@other.host
#luser_relay = $local@other.host
#luser_relay = admin+$local

# JUNK MAIL CONTROLS
#
# The controls listed here are only a very small subset. The file
# SMTPD_ACCESS_README provides an overview.

# The header_checks parameter specifies an optional table with patterns
# that each logical message header is matched against, including
# headers that span multiple physical lines.
#
# By default, these patterns also apply to MIME headers and to the
# headers of attached messages. With older Postfix versions, MIME and
# attached message headers were treated as body text.
#
# For details, see "man header_checks".
#
#header_checks = regexp:/etc/postfix/header_checks

# FAST ETRN SERVICE
#
# Postfix maintains per-destination logfiles with information about
# deferred mail, so that mail can be flushed quickly with the SMTP
# "ETRN domain.tld" command, or by executing "sendmail -qRdomain.tld".
# See the ETRN_README document for a detailed description.
#
# The fast_flush_domains parameter controls what destinations are
# eligible for this service. By default, they are all domains that
# this server is willing to relay mail to.
#
#fast_flush_domains = $relay_domains

# SHOW SOFTWARE VERSION OR NOT
#
# The smtpd_banner parameter specifies the text that follows the 220
# code in the SMTP server's greeting banner. Some people like to see
# the mail version advertised. By default, Postfix shows no version.
#
# You MUST specify $myhostname at the start of the text. That is an
# RFC requirement. Postfix itself does not care.
#
#smtpd_banner = $myhostname ESMTP $mail_name
#smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

# PARALLEL DELIVERY TO THE SAME DESTINATION
#
# How many parallel deliveries to the same user or domain? With local
# delivery, it does not make sense to do massively parallel delivery
# to the same user, because mailbox updates must happen sequentially,
# and expensive pipelines in .forward files can cause disasters when
# too many are run at the same time. With SMTP deliveries, 10
# simultaneous connections to the same domain could be sufficient to
# raise eyebrows.
#
# Each message delivery transport has its XXX_destination_concurrency_limit
# parameter. The default is $default_destination_concurrency_limit for
# most delivery transports. For the local delivery agent the default is 2.

#local_destination_concurrency_limit = 2
#default_destination_concurrency_limit = 20

# DEBUGGING CONTROL
#
# The debug_peer_level parameter specifies the increment in verbose
# logging level when an SMTP client or server host name or address
# matches a pattern in the debug_peer_list parameter.
#
debug_peer_level = 2

# The debug_peer_list parameter specifies an optional list of domain
# or network patterns, /file/name patterns or type:name tables. When
# an SMTP client or server host name or address matches a pattern,
# increase the verbose logging level by the amount specified in the
# debug_peer_level parameter.
#
#debug_peer_list = 127.0.0.1
#debug_peer_list = some.domain

# The debugger_command specifies the external command that is executed
# when a Postfix daemon program is run with the -D option.
#
# Use "command .. & sleep 5" so that the debugger can attach before
# the process marches on. If you use an X-based debugger, be sure to
# set up your XAUTHORITY environment variable before starting Postfix.
#
debugger_command =
PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
xxgdb $daemon_directory/$process_name $process_id & sleep 5

# If you can't use X, use this to capture the call stack when a
# daemon crashes. The result is in a file in the configuration
# directory, and is named after the process name and the process ID.
#
# debugger_command =
# PATH=/bin:/usr/bin:/usr/local/bin; export PATH; (echo cont;
# echo where) | gdb $daemon_directory/$process_name $process_id 2>&1
# >$config_directory/$process_name.$process_id.log & sleep 5
#
# Another possibility is to run gdb under a detached screen session.
# To attach to the screen sesssion, su root and run "screen -r
# <id_string>" where <id_string> uniquely matches one of the detached
# sessions (from "screen -list").
#
# debugger_command =
# PATH=/bin:/usr/bin:/sbin:/usr/sbin; export PATH; screen
# -dmS $process_name gdb $daemon_directory/$process_name
# $process_id & sleep 1

# INSTALL-TIME CONFIGURATION INFORMATION
#
# The following parameters are used when installing a new Postfix version.
#
# sendmail_path: The full pathname of the Postfix sendmail command.
# This is the Sendmail-compatible mail posting interface.
#
sendmail_path = /usr/sbin/sendmail.postfix

# newaliases_path: The full pathname of the Postfix newaliases command.
# This is the Sendmail-compatible command to build alias databases.
#
newaliases_path = /usr/bin/newaliases.postfix

# mailq_path: The full pathname of the Postfix mailq command. This
# is the Sendmail-compatible mail queue listing command.
#
mailq_path = /usr/bin/mailq.postfix

# setgid_group: The group for mail submission and queue management
# commands. This must be a group name with a numerical group ID that
# is not shared with other accounts, not even with the Postfix account.
#
setgid_group = postdrop

# html_directory: The location of the Postfix HTML documentation.
#
html_directory = no

# manpage_directory: The location of the Postfix on-line manual pages.
#
manpage_directory = /usr/share/man

# sample_directory: The location of the Postfix sample configuration files.
# This parameter is obsolete as of Postfix 2.1.
#
sample_directory = /usr/share/doc/postfix-2.3.3/samples

# readme_directory: The location of the Postfix README files.
#
readme_directory = /usr/share/doc/postfix-2.3.3/README_FILES

[root@zen postfix]# postconf -n
alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
debug_peer_level = 2
html_directory = no
inet_interfaces = $myhostname, localhost
mail_owner = postfix
mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
mydestination = $myhostname, localhost.$mydomain, localhost
mynetworks_style = host
newaliases_path = /usr/bin/newaliases.postfix
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.3.3/README_FILES
relayhost = slave.37chapellane.co.uk
sample_directory = /usr/share/doc/postfix-2.3.3/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
unknown_local_recipient_reject_code = 550

Agreed. You're going to get lots of undeliverable messages if anyone decides to use your domain name to spoof as their "from" address to send spam.

As for sending out 300 messages... could you show a few dozen lines from the Postfix log (usually something like /var/log/maillog, /var/log/mail.log, /var/log/mail.somethingorother)? Actually, I think grep'ing for "relay=" should give the appropriate output.

mynetworks = host means that only the local machine can send mail through this setup, so relaying shouldn't be an issue unless I'm missing something

if you've got any webserver on that machine, which serves any dumbass php/cgi that may be able to send mails - u've got ur bugger!