Re: reject_unknown_reverse_client_hostname safe?
- On 05/08/2013 08:03 PM, Stan Hoeppner wrote:
> On 5/7/2013 5:36 PM, /dev/rob0 wrote:No, they have to match, I'll go into detail so that hopefully you
>> Peter has explained this: you indeed seem to have FCrDNS, just not
> Maybe my understanding of the definition of Forward Confirmed reverse
> DNS is incorrect. I thought the definition of FCrDNS is that that the
> forward and reverse names not only exist but also match. Apparently
> they both must simply exist.
Your host claims to be greer.hardwarefreak.com and connects from the IP
220.127.116.11, so first we do a lookup on your hostname:
> greer.hardwarefreak.com. 3448 IN A 18.104.22.168...it matches the IP of your connection ... This is good.
Next we do a reverse lookup on the IP:
> 22.214.171.124.in-addr.arpa. 86176 IN PTR mo-65-41-216-221.sta.embarqhsd.net.This doesn't return your initial hostname, but that's ok because that is
not specifically required for FCRDNS. What is required at this stage is
that the PTR lookup return a valid FQDN and it does indeed.
Note that the FQDN that is returned "looks" like a generic ISP-assigned
hostname (because of the IP address in the name). This isn't a good
thing and there are some mail hosts that will reject based on this, but
very few in my experience. That generic-looking hostname does not mean
that it won't pass FCRDNS, though.
Ok, next we do a lookup on the hostname we got back from the previous step:
> mo-65-41-216-221.sta.embarqhsd.net. 86166 IN A 126.96.36.199...this returns your IP address as well, and that is good because this
is required for FCRDNS.
- On 5/14/2013 11:45 AM, Steve Jenkins wrote:
> On Tue, May 14, 2013 at 8:33 AM, /dev/rob0 <rob0@...> wrote:"permits" always come before "rejects". Thus whitelist type entries
>> On Tue, May 14, 2013 at 07:49:50AM -0700, Steve Jenkins wrote:
>>> smtpd_recipient_restrictions =
>>> warn_if_reject reject_non_fqdn_helo_hostname,
>>> warn_if_reject reject_unknown_helo_hostname,
>>> check_helo_access hash:/etc/postfix/helo_access,
>>> check_sender_access hash:/etc/postfix/sender_access,
>>> reject_rbl_client zen.spamhaus.org,
>>> reject_rhsbl_client dbl.spamhaus.org,
>>> reject_rhsbl_sender dbl.spamhaus.org,
>>> reject_rhsbl_helo dbl.spamhaus.org,
>>> permit_dnswl_client list.dnswl.org=127.0.[0..255].[1..3],
>> The last two lines are no-op. If you have anything you want to be
>> subjected to the list.dnswl.org whitelist, put it after the
>> permit_dnswl_client. If not, there is no point in querying it.
> Excellent point. If the next step is going to "permit" anyway, then no use
> in the extra query. I've moved the dnswl.org line up so that it's just
> above the three "local" check_* lines.
should always be at the top of the restrictions list. As you are using
(client|helo|sender|recipient) sections any whitelisting in
smtpd_recipient_restrictions should typically be at the very top.
This shows you are explicitly permitting anything/everything listed in
the dnswl. Are you sure that is what you want? I use...
which does not explicitly permit email marketing providers nor any IP
with trustworthiness score of 1. A score of 1 is equivalent to a
SpamAssassin score of -1, which does not merit a direct shot to the
queue. That would typically require an SA score of -5. I want these
clients to go through all of my other restrictions before allowing their
payload into my queue.
Also worth noting, there are currently only 14 categories (3rd octet of
a reply), so specifying 255 is not necessary, and possibly problematic.
Hypothetically, if dnswl decided one day to create categories 16,
political campaigns, and 17, religious newsletters, you are currently
setup to automatically permit such clients.
Remember, the sole purpose of whitelisting is to bypass all of your
other spam checks and get the mail into your queue unmolested. IMO, not
every IP listed by dnswl is deserving of this honor, not even close to
all of them.
See section "Return codes" at: http://www.dnswl.org/tech