Filter replacement on Dyson HP02

Note to self: to replace the filter on a Dyson HP02:

  1. Turn off and unplug the Dyson HP02 unit.
  2. Remove the filter. Turn the base of the machine to access the filter. Then press the two buttons on the sides of the machine to release the filter.
  3. Clean or replace the filter. You can wash the filter with cold water. Do not use detergent or soap. Rinse the filter under the water until it’s clean and then let it dry for at least 24 hours in a warm place. It’s important that it’s completely dry before you put it back into the machine. If the filter is too dirty or damaged, it might be best to replace it with a new one.
  4. Replace the filter. Once the filter is completely dry, place it back in the machine. It should click into place.
  5. Reset the filter indicator. Plug in and turn on your device. Hold down the ‘standby ON/OFF’ button for 6 seconds on the remote to reset the filter indicator.

Note: you hold down the button on the *remote* not on the unit itself.

Postfix Virtual Mailboxes and Procmail Filtering

Am interested in getting procmail to work with my Postfix/Courier setup. Am using virtual domains/aliases/mailboxes stored in a MySQL database and a Maildir file system. Have only just begun my investigations. So far I’ve found:

SpamAssassin whitelist and blacklisting

Today I figured out how to specify whitelist and blacklist email addresses in SpamAssassin.

At the end of /etc/spamassassin/ I added two lines:

include whitelist
include blacklist

Then in the /etc/spamassassin/whitelist file I added some email specifications, e.g.:

jj5@sixsigma:~$ cat /etc/spamassassin/whitelist
# Allow email from system services, e.g. from
# or
whitelist_from *@*.progclub.*
# Similarly for blackbrick:
whitelist_from *@*

The /etc/spamassassin/blacklist file exists and is ready to go, but I haven’t blacklisted anything yet:

jj5@sixsigma:~$ cat /etc/spamassassin/blacklist
# No email addresses blacklisted yet.

Too easy.

There’s some more information on Whitelising a user.

At some point I hope to write a script that processes my users’ maildirs and whitelists everyone they’ve emailed.


Tonight I read the FILTER_README file from Postfix.


This is a very first implementation of Postfix content filtering.
A Postfix content filter receives unfiltered mail from Postfix and
does one of the following:

- re-injects the mail back into Postfix, perhaps after changing content
- rejects the mail (by sending a suitable status code back to
  Postfix) so that it is returned to sender.
- sends the mail somewhere else

This document describes two approaches to content filtering: simple
and advanced. Both filter all the mail by default.

At the end are examples that show how to filter only mail from
users, about using different filters for different domains that
you provide MX service for, and about selective filtering on the
basis of message envelope and/or header/body patterns.

Simple content filtering example

The first example is simple to set up.  It uses a shell script that
receives unfiltered mail from the Postfix pipe delivery agent, and
that feeds filtered mail back into the Postfix sendmail command.

Only mail arriving via SMTP will be content filtered.

                  :            Postfix             :
Unfiltered mail----->smtpd \                /local---->Filtered mail
                  :         -cleanup->queue-       :
               ---->pickup /                \smtp----->Filtered mail
               ^  :                        |       :
               |  :                         \pipe-----+
               |  ..................................  |
               |                                      |
               |                                      |
               +-Postfix sendmail<----filter script<--+

Mail is filtered by a /some/where/filter program. This can be a
simple shell script like this:


    # Localize these.
    SENDMAIL="/usr/sbin/sendmail -i"

    # Exit codes from <sysexits.h>

    # Clean up when done or when aborting.
    trap "rm -f in.$$" 0 1 2 3 15

    # Start processing.
    cd $INSPECT_DIR || { echo $INSPECT_DIR does not exist; exit $EX_TEMPFAIL; }

    cat >in.$$ || { echo Cannot save mail to file; exit $EX_TEMPFAIL; }

    # filter <in.$$ || { echo Message content rejected; exit $EX_UNAVAILABLE; }

    $SENDMAIL "$@" <in.$$

    exit $?

The idea is to first capture the message to file and then run the
content through a third-party content filter program.

- If the mail cannot be captured to file, mail delivery is deferred
  by terminating with exit status 75 (EX_TEMPFAIL). Postfix will
  try again after some delay.

- If the content filter program finds a problem, the mail is bounced
  by terminating with exit status 69 (EX_UNAVAILABLE).  Postfix
  will return the message to the sender as undeliverable.

- If the content is OK, it is given as input to the Postfix sendmail
  command, and the exit status of the filter command is whatever
  exit status the Postfix sendmail command produces. Postfix will
  deliver the message as usual.

I suggest that you run this script by hand until you are satisfied
with the results. Run it with a real message (headers+body) as

    % /some/where/filter -f sender recipient... <message-file

Once you're satisfied with the content filtering script:

1 - Create a dedicated local user account called "filter".  This
    user handles all potentially dangerous mail content - that is
    why it should be a separate account. Do not use "nobody", and
    most certainly do not use "root" or "postfix".  The user will
    never log in, and can be given a "*" password and non-existent
    shell and home directory.

2 - Create a directory /var/spool/filter that is accessible only
    to the "filter" user. This is where the content filtering script
    is supposed to store its temporary files.

3 - Define the content filter in the Postfix master file:

      filter    unix  -       n       n       -       -       pipe
        flags=Rq user=filter argv=/somewhere/filter -f ${sender} -- ${recipient}

To turn on content filtering for mail arriving via SMTP only, append
"-o content_filter=filter:dummy" to the entry that defines
the Postfix SMTP server:

        smtp      inet     ...stuff...      smtpd
            -o content_filter=filter:dummy

The content_filter configuration parameter accepts the same syntax
as the right-hand side in a Postfix transport table.  Execute
"postfix reload" to complete the change.

To turn off content filtering, edit the file, remove the
"-o content_filter=filter:dummy" text from the entry that defines
the Postfix SMTP server, and execute another "postfix reload".

With the shell script as shown above you will lose a factor of four
in Postfix performance for transit mail that arrives and leaves
via SMTP. You will lose another factor in transit performance for
each additional temporary file that is created and deleted in the
process of content filtering.  The performance impact is less for
mail that is submitted or delivered locally, because such deliveries
are already slower than SMTP transit mail.

Simple content filter limitations

The problem with content filters like the one above is that they
are not very robust. The reason is that the software does not talk
a well-defined protocol with Postfix. If the filter shell script
aborts because the shell runs into some memory allocation problem,
the script will not produce a nice exit status as defined in the
file /usr/include/sysexits.h.  Instead of going to the deferred
queue, mail will bounce.  The same lack of robustness can happen
when the content filtering software itself runs into a resource

Advanced content filtering example

The second example is more complex, but can give much better
performance, and is less likely to bounce mail when the machine
runs into a resource problem.  This approach uses content filtering
software that can receive and deliver mail via SMTP.

Some Anti-virus software is built to receive and deliver mail via
SMTP and is ready to use as an advanced Postfix content filter.
For non-SMTP capable content filtering software, Bennett Todd's
SMTP proxy implements a nice PERL/SMTP content filtering framework.

The example given here filters all mail, including mail that arrives
via SMTP and mail that is locally submitted via the Postfix sendmail

You can expect to lose about a factor of two in Postfix performance
for transit mail that arrives and leaves via SMTP, provided that
the content filter creates no temporary files. Each temporary file
created by the content filter adds another factor to the performance

We will set up a content filtering program that receives SMTP mail
via localhost port 10025, and that submits SMTP mail back into
Postfix via localhost port 10026.

      :            Postfix             :
   ----->smtpd \                /local---->
      :         -cleanup->queue-       :
   ---->pickup /    ^       |   \smtp----->
      :             |       v          :
      :           smtpd    smtp        :
      :           10026     |          :
                    ^       |
                    |       v
                :   |     10025 :
                :   filter      :
                :               :

To enable content filtering in this manner, specify in a
new parameter:

        content_filter = scan:localhost:10025

This causes Postfix to add one extra content filtering record to
each incoming mail message, with content scan:localhost:10025.
The content filtering records are added by the smtpd and pickup

When a queue file has content filtering information, the queue
manager will deliver the mail to the specified content filter
regardless of its final destination.

In this example, "scan" is an instance of the Postfix SMTP client
with slightly different configuration parameters. This is how
one would set up the service in the Postfix file:

        scan      unix  -       -       n       -       10       smtp

Instead of a limit of 10 concurrent processes, use whatever process
limit is feasible for your machine.  Content inspection software
can gobble up a lot of system resources, so you don't want to have
too much of it running at the same time.

The content filter can be set up with the Postfix spawn service,
which is the Postfix equivalent of inetd. For example, to instantiate
up to 10 content filtering processes on demand:

        localhost:10025     inet  n      n      n      -      10     spawn
            user=filter argv=/some/where/filter localhost 10026

"filter" is a dedicated local user account.  The user will never
log in, and can be given a "*" password and non-existent shell and
home directory.  This user handles all potentially dangerous mail
content - that is why it should be a separate account.

In the above example, Postfix listens on port localhost:10025.  If
you want to have your filter listening on port localhost:10025
instead of Postfix, then you must run your filter as a stand-alone

Note: the localhost port 10025 SMTP server filter should announce
itself as "220 localhost...".  Postfix aborts delivery when it
connects to an SMTP server that uses the same hostname as Postfix
("host <servername> greeted me with my own hostname"), because that
normally means you have a mail delivery loop problem.

The example here assumes that the /some/where/filter command is a
PERL script. PERL has modules that make talking SMTP easy. The
command-line specifies that mail should be sent back into Postfix
via localhost port 10026.

The simplest content filter just copies SMTP commands and data
between its inputs and outputs. If it has a problem, all it has to
do is to reply to an input of `.' with `550 content rejected', and
to disconnect without sending `.' on the connection that injects
mail back into Postfix.

The job of the content filter is to either bounce mail with a
suitable diagnostic, or to feed the mail back into Postfix through
a dedicated listener on port localhost 10026:

        localhost:10026     inet  n      -      n      -      10      smtpd
            -o content_filter=
            -o local_recipient_maps=
            -o relay_recipient_maps=
            -o myhostname=localhost.domain.tld
            -o smtpd_helo_restrictions=
            -o smtpd_client_restrictions=
            -o smtpd_sender_restrictions=
            -o smtpd_recipient_restrictions=permit_mynetworks,reject
            -o mynetworks=

Warning for Postfix version 2 users: in this SMTP server after the
content filter, do not override settings for virtual_alias_maps
or virtual_alias_domains. That would cause mail to be rejected with
"User unknown".

This SMTP server has the same process limit as the "filter"

The "-o content_filter=" requests no content filtering for incoming

The "-o local_recipient_maps=" and "-o relay_recipient_maps=" avoid
unnecessary table lookups.

The "-o myhostname=localhost.domain.tld" avoids false alarms ("host
<servername> greeted me with my own hostname") if your content
filter is based on a proxy that simply relays SMTP commands.

The "-o smtpd_xxx_restrictions" and "-o mynetworks="
turn off UCE controls that would only waste time here.

Squeezing out more performance

Many refinements are possible, such as running a specially-configured
smtp delivery agent for feeding mail into the content filter, and
turning off address rewriting before content filtering.

As the example below shows, things quickly become very complex,
because a lot of like information gets listed in the file. This makes the system hard to understand.

Even worse, details change as Postfix evolves and different
configuration parameters are implemented by different programs.

If you need to squeeze out more performance, it is probably simpler
to run multiple Postfix instances, one before and one after the
content filter. That way, each instance can have simple
and files, each instance can have its own mail queue,
and the system will be easier to understand.

As before, we will set up a content filtering program that receives
SMTP mail via localhost port 10025, and that submits SMTP mail back
into Postfix via localhost port 10026.

      :                Postfix              :
   ----->smtpd \                            :
      :         -pre-cleanup-\       /local---->
   ---->pickup /              -queue-       :
      :             -cleanup-/   |   \smtp----->
      :     bounces/    ^        v          :
      : and locally     |        v          :
      :   forwarded   smtpd     scan        :
      :    messages   10026      |          :
                        ^        |
                        |        v
                    :   |      10025 :
                    :   filter       :
                    :                :

To enable content filtering in this manner, specify in a
new parameter:

    content_filter = scan:localhost:10025

# These are the usual input "smtpd" and local "pickup" servers already
# present in We add an option to select a non-default
# cleanup service (defined further below).
smtp      inet  n       -       n       -       -       smtpd
    -o cleanup_service_name=pre-cleanup
pickup    fifo  n       -       n       60      1       pickup
    -o cleanup_service_name=pre-cleanup
# ------------------------------------------------------------------
# This is the cleanup daemon that handles messages in front of
# the content filter. It does header_checks and body_checks (if
# any), but does no virtual alias or canonical address mapping,
# so that mail passes through your content filter with the original
# recipient addresses mostly intact.
# Virtual alias or canonical address mapping happens in the second
# cleanup phase after the content filter. This gives the content_filter
# access to *largely* unmodified addresses for maximum flexibility.
# Some sites may specifically want to perform canonical or virtual
# address mapping in front of the content_filter.  In that case you
# still have to enable address rewriting in the after-filter cleanup
# instance, in order to correctly process forwarded mail or bounced
# mail.
pre-cleanup         unix  n      -      n      -       0      cleanup
        -o canonical_maps=
        -o sender_canonical_maps=
        -o recipient_canonical_maps=
        -o masquerade_domains=
        -o virtual_alias_maps=
# ------------------------------------------------------------------
# This is the delivery agent that injects mail into the content
# filter.  It is tuned for low concurrency, because most content
# filters burn CPU and use lots of memory.  The process limit of 10
# re-enforces the effect of $default_destination_concurrency_limit.
# Even without an explicit process limit, the concurrency is bounded
# because all messages heading into the content filter have the same
# destination.
scan                unix  -      -      n      -      10      smtp
# ------------------------------------------------------------------
# This is the SMTP listener that receives filtered messages from
# the content filter. It *MUST* clear the content_filter
# parameter to avoid loops, and use a different hostname to avoid
# triggering the Postfix SMTP loop detection code.
# This "smtpd" uses the normal cleanup service which is also used
# for bounces and for internally forwarded mail.
# The parameters from mynetworks onward disable all access
# control other than insisting on connections from one of the IP
# addresses of the host. This is typically overkill, but can
# reduce resource usage, if the default restrictions use lots of
# tables.
localhost:10026     inet  n      -      n      -       -      smtpd
    -o content_filter=
    -o myhostname=localhost.domain.tld
    -o local_recipient_maps=
    -o relay_recipient_maps=
    -o mynetworks=
    -o mynetworks_style=host
    -o smtpd_restriction_classes=
    -o smtpd_client_restrictions=
    -o smtpd_helo_restrictions=
    -o smtpd_sender_restrictions=
    -o smtpd_recipient_restrictions=permit_mynetworks,reject
# Do not override settings here for virtual_alias_maps or
# virtual_mailbox_maps. This causes mail to be rejected with "User
# unknown in virtual (alias|mailbox) recipient table".
# ------------------------------------------------------------------
# This is the normal cleanup daemon for use after content filtering.
# No header or body checks, because those have already been taken
# care of by the pre-cleanup service before the content filter.
# The normal cleanup instance does all the virtual alias and canonical
# address mapping that was disabled in the pre-cleanup instance before
# the content filter. This rewriting must be done even when you didn't
# disable address rewriting in the pre-cleanup instance, in order to
# correctly process bounces and locally forwarded mail.
cleanup            unix  n      -      n      -       0      cleanup
    -o header_checks=
    -o mime_header_checks=
    -o nested_header_checks=
    -o body_checks=
# ------------------------------------------------------------------
# The normal "smtp" delivery agent for contrast with "scan".
smtp                unix  -      -      n      -      -       smtp

The above example causes Postfix to add one content filtering record
to each incoming mail message, with content scan:localhost:10025.
You can use the same syntax as in the right-hand side of a Postfix
transport table.  The content filtering records are added by the
smtpd and pickup servers.

The "scan" transport is a dedicated instance of the "smtp" delivery
agent for injecting messages into the SMTP content filter. Using
a dedicated "smtp" transport allows one to tune it for the specific
task of delivering mail to a local content filter (low latency,
low concurrency, throughput dependent on predictably low latency).

See the previous example for setting up the content filter with
the Postfix spawn service; you can of course use any server that
can be run stand-alone outside the Postfix environment.

Filtering mail from outside users only

The easiest approach is to configure ONE Postfix instance with TWO
SMTP server addresses in

- One SMTP server address for inside users only that never invokes
  content filtering.

- One SMTP server address for outside users that always invokes
  content filtering.

    # SMTP service for internal users only, no content filtering.        inet  n       -       n       -       -       smtpd
        -o smtpd_client_restrictions=permit_mynetworks,reject      inet  n       -       n       -       -       smtpd
        -o smtpd_client_restrictions=permit_mynetworks,reject

    # SMTP service for external users, with content filtering.        inet  n       -       n       -       -       smtpd
        -o content_filter=foo:bar

Getting really nasty

The above filtering configurations are static. Mail that follows
a given path is either always filtered or it is never filtered. As
of Postfix 2.0 you can also turn on content filtering on the fly.
The Postfix UCE features allow you to specify a filtering action
on the fly:

    FILTER foo:bar

You can do this in smtpd access maps as well as the cleanup server's
header/body_checks.  This feature must be used with great care:
you must disable all the UCE features in the after-filter smtpd
and cleanup daemons or else you will have a content filtering loop.


- There can be only one content filter action per message.

- FILTER actions from smtpd access maps and header/body_checks take
  precedence over filters specified with the content_filter

- Only the last FILTER action from smtpd access maps or from
  header/body_checks takes effect.

- The same content filter is applied to all the recipients of a
  given message.

Postfix header checks

I wanted to do something about the fact that I get a lot of spam where the date is substantially in the past, that is, months or years ago.

I figure I’ll never get any mail that I care about where the date is set that far back so what I wanted was a way to filter out such email.

There didn’t seem to be any suitable option in Thunderbird, and I’d rather have this done on the server than the client anyway, so I started fishing around for options in Postfix.

I found out about header checks.

To enable I had to add a file to the header_checks configuration option in /etc/postfix/

header_checks =

Then I created a header_filter_map file with some regexes for the date:

/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 1\d\d\d/ DISCARD Date 1
/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 200\d/ DISCARD Date 2
/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 201[0-1]/ DISCARD Date 3
/^Date: .* Jan 2012/ DISCARD Date Jan
/^Date: .* Feb 2011/ DISCARD Date Feb
/^Date: .* Mar 2011/ DISCARD Date Mar
/^Date: .* Apr 2011/ DISCARD Date Apr
/^Date: .* May 2011/ DISCARD Date May
/^Date: .* Jun 2011/ DISCARD Date Jun
/^Date: .* Jul 2011/ DISCARD Date Jul
/^Date: .* Aug 2011/ DISCARD Date Aug
/^Date: .* Sep 2011/ DISCARD Date Sep
/^Date: .* Oct 2011/ DISCARD Date Oct
/^Date: .* Nov 2011/ DISCARD Date Nov
/^Date: .* Dec 2011/ DISCARD Date Dec

I also found this file so I added some rules for the X-Mailer header, like this:

/^X-Mailer: 0001/                               DISCARD Mailer 1
/^X-Mailer: Avalanche/                          DISCARD Mailer 2
/^X-Mailer: Crescent Internet Tool/             DISCARD Mailer 3
/^X-Mailer: DiffondiCool/                       DISCARD Mailer 4
/^X-Mailer: E-Mail Delivery Agent/              DISCARD Mailer 5
/^X-Mailer: Emailer Platinum/                   DISCARD Mailer 6
/^X-Mailer: Entity/                             DISCARD Mailer 7
/^X-Mailer: Extractor/                          DISCARD Mailer 8
/^X-Mailer: Floodgate/                          DISCARD Mailer 9
/^X-Mailer: GOTO Software Sarbacane/            DISCARD Mailer 10
/^X-Mailer: MailWorkz/                          DISCARD Mailer 11
/^X-Mailer: MassE-Mail/                         DISCARD Mailer 12
/^X-Mailer: MaxBulk.Mailer/                     DISCARD Mailer 13
/^X-Mailer: News Breaker Pro/                   DISCARD Mailer 14
/^X-Mailer: SmartMailer/                        DISCARD Mailer 15
/^X-Mailer: StormPort/                          DISCARD Mailer 16
/^X-Mailer: SuperMail-2/                        DISCARD Mailer 17

Now that I know how to do this I’ll start adding rules for particular spam that I seem to get a lot of.

I’m not sure if I made the best decision, but I decided to silently discard email rather than reject it.

Ignoring emails with old dates

I was reading about Postfix’s cleanup facility which supports header_checks which can be specified in a regexp: table. And it inspired me to come up with this header_filter_map file:

/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 1/ REJECT
/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 200/ REJECT
/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 2010/ REJECT
/^Date: .* [JFMASOND][aepuco][nbrynlgptvc] 2011/ REJECT
/^Date: .* Jan 2012/ REJECT
/^Date: .* Feb 2011/ REJECT
/^Date: .* Mar 2011/ REJECT
/^Date: .* Apr 2011/ REJECT
/^Date: .* May 2011/ REJECT
/^Date: .* Jun 2011/ REJECT
/^Date: .* Jul 2011/ REJECT
/^Date: .* Aug 2011/ REJECT
/^Date: .* Sep 2011/ REJECT
/^Date: .* Oct 2011/ REJECT
/^Date: .* Nov 2011/ REJECT
/^Date: .* Dec 2011/ REJECT

Which I applied in Postfix by adding the following line to /etc/postfix/

header_checks = regexp:/etc/postfix/header_filter_map

It remains to be seen if what I’ve done will work, and at the moment this is a bit of a pain because I have to manually update the header_filter_map file every month, but the general idea is that if the regexp matches a date too far in the past then the message is rejected. Hopefully then those spammers who have messages turning up in my history will be gone.

WordPress hooks

I wanted to configure the “From” email address that WordPress uses when emailing password resets. The way to do this is with a WordPress hook, specifically a filter hook in this case. So, in wp-config.php I added the following code:

add_filter( 'wp_mail_from', 'pcblog_mail_from' );
add_filter( 'wp_mail_from_name', 'pcblog_mail_from_name' );

function pcblog_mail_from() {
  return '';
function pcblog_mail_from_name() {
  return 'ProgClub blog';