Digging on FILTER_README, I've noticed that:
> The content_filter setting has lower precedence than a FILTER
action that is specified in an access(5), header_checks(5) or
body_checks(5) table.
Even using OK, PREPEND, the message could not go back into queue.
JIT:
ACCEPT ACTIONS
OK Accept the address etc. that matches the pattern.
all-numerical
An all-numerical result is treated as OK. This format is gener-
ated by address-based relay authorization schemes such as
pop-before-smtp.
For other accept actions, see "OTHER ACTIONS" below.
REJECT ACTIONS
Postfix version 2.3 and later support enhanced status codes as defined
in RFC 3463. When no code is specified at the beginning of the text
below, Postfix inserts a default enhanced status code of "5.7.1" in the
case of reject actions, and "4.7.1" in the case of defer actions. See
"ENHANCED STATUS CODES" below.
4NN text
5NN text
Reject the address etc. that matches the pattern, and respond
with the numerical three-digit code and text. 4NN means "try
again later", while 5NN means "do not try again".
The following responses have special meaning for the Postfix
SMTP server:
421 text (Postfix 2.3 and later)
521 text (Postfix 2.6 and later)
After responding with the numerical three-digit code and
text, disconnect immediately from the SMTP client. This
frees up SMTP server resources so that they can be made
available to another SMTP client.
Note: The "521" response should be used only with botnets
and other malware where interoperability is of no con-
cern. The "send 521 and disconnect" behavior is NOT
defined in the SMTP standard.
REJECT optional text...
Reject the address etc. that matches the pattern. Reply with
"$access_map_reject_code optional text..." when the optional
text is specified, otherwise reply with a generic error response
message.
DEFER optional text...
Reject the address etc. that matches the pattern. Reply with
"$access_map_defer_code optional text..." when the optional text
is specified, otherwise reply with a generic error response mes-
sage.
This feature is available in Postfix 2.6 and later.
DEFER_IF_REJECT optional text...
Defer the request if some later restriction would result in a
REJECT action. Reply with "$access_map_defer_code 4.7.1 optional
text..." when the optional text is specified, otherwise reply
with a generic error response message.
Prior to Postfix 2.6, the SMTP reply code is 450.
This feature is available in Postfix 2.1 and later.
DEFER_IF_PERMIT optional text...
Defer the request if some later restriction would result in a an
explicit or implicit PERMIT action. Reply with
"$access_map_defer_code 4.7.1 optional text..." when the
optional text is specified, otherwise reply with a generic error
response message.
Prior to Postfix 2.6, the SMTP reply code is 450.
This feature is available in Postfix 2.1 and later.
For other reject actions, see "OTHER ACTIONS" below.
OTHER ACTIONS
restriction...
Apply the named UCE restriction(s) (permit, reject,
reject_unauth_destination, and so on).
BCC user@domain
Send one copy of the message to the specified recipient.
If multiple BCC actions are specified within the same SMTP MAIL
transaction, with Postfix 3.0 only the last action will be used.
This feature is available in Postfix 3.0 and later.
DISCARD optional text...
Claim successful delivery and silently discard the message. Log
the optional text if specified, otherwise log a generic message.
Note: this action currently affects all recipients of the mes-
sage. To discard only one recipient without discarding the
entire message, use the transport(5) table to direct mail to the
discard(8) service.
This feature is available in Postfix 2.0 and later.
DUNNO Pretend that the lookup key was not found. This prevents Postfix
from trying substrings of the lookup key (such as a subdomain
name, or a network address subnetwork).
This feature is available in Postfix 2.0 and later.
FILTER transport:destination
After the message is queued, send the entire message through the
specified external content filter. The transport name specifies
the first field of a mail delivery agent definition in mas-
ter.cf; the syntax of the next-hop destination is described in
the manual page of the corresponding delivery agent. More
information about external content filters is in the Postfix
FILTER_README file.
Note 1: do not use $number regular expression substitutions for
transport or destination unless you know that the information
has a trusted origin.
Note 2: this action overrides the main.cf content_filter set-
ting, and affects all recipients of the message. In the case
that multiple FILTER actions fire, only the last one is exe-
cuted.
Note 3: the purpose of the FILTER command is to override message
routing. To override the recipient's transport but not the
next-hop destination, specify an empty filter destination (Post-
fix 2.7 and later), or specify a transport:destination that
delivers through a different Postfix instance (Postfix 2.6 and
earlier). Other options are using the recipient-dependent trans-
port_maps or the sender-dependent sender_dependent_default-
_transport_maps features.
This feature is available in Postfix 2.0 and later.
HOLD optional text...
Place the message on the hold queue, where it will sit until
someone either deletes it or releases it for delivery. Log the
optional text if specified, otherwise log a generic message.
Mail that is placed on hold can be examined with the postcat(1)
command, and can be destroyed or released with the postsuper(1)
command.
Note: use "postsuper -r" to release mail that was kept on hold
for a significant fraction of $maximal_queue_lifetime or
$bounce_queue_lifetime, or longer. Use "postsuper -H" only for
mail that will not expire within a few delivery attempts.
Note: this action currently affects all recipients of the mes-
sage.
This feature is available in Postfix 2.0 and later.
PREPEND headername: headervalue
Prepend the specified message header to the message. When more
than one PREPEND action executes, the first prepended header
appears before the second etc. prepended header.
Note: this action must execute before the message content is
received; it cannot execute in the context of
smtpd_end_of_data_restrictions.
This feature is available in Postfix 2.1 and later.
REDIRECT user@domain
After the message is queued, send the message to the specified
address instead of the intended recipient(s). When multiple RE-
DIRECT actions fire, only the last one takes effect.
Note: this action overrides the FILTER action, and currently
overrides all recipients of the message.
This feature is available in Postfix 2.1 and later.
INFO optional text...
Log an informational record with the optional text, together
with client information and if available, with helo, sender,
recipient and protocol information.
This feature is available in Postfix 3.0 and later.
WARN optional text...
Log a warning with the optional text, together with client
information and if available, with helo, sender, recipient and
protocol information.
This feature is available in Postfix 2.1 and later.
BR
Rafael
