On 2021-05-22 at 03:33:37 UTC-0400 (Sat, 22 May 2021 17:33:37 +1000)
Simon Wilson <[email protected]>
is rumored to have said:
Question about one of those services that validates email addresses on
the fly when you fill in a form...
There is one (Briteverify) which seems to fail email addresses at our
postfix server for an unknown reason.
Let's start with 2 stipulations:
1. Briteverify has a history as an abusive facilitator of spammers. They
have a history of attempting to verify bogus addresses harvested from
things like ancient Usenet message IDs at DoS rates. Whether they are
still doing that, I cannot say for sure, but they have been a bad actor
in the past.
2. Everything I postulate below are educated guesses.
I put my email in the form (it's used by a local food delivery
service), and in the background I see this on my server:
May 22 17:17:44 emp87 postfix/postscreen[805286]: CONNECT from
[184.72.250.175]:35556 to [192.168.1.230]:25
May 22 17:17:44 emp87 postfix/postscreen[805286]: CONNECT from
[107.20.235.139]:41162 to [192.168.1.230]:25
May 22 17:17:44 emp87 postfix/dnsblog[805300]: addr 184.72.250.175
listed by domain hostkarma.junkemailfilter.com as 127.0.1.1
May 22 17:17:44 emp87 postfix/dnsblog[805318]: addr 107.20.235.139
listed by domain hostkarma.junkemailfilter.com as 127.0.1.1
May 22 17:17:49 emp87 postfix/postscreen[805286]: HANGUP after 5.2
from [184.72.250.175]:35556 in tests before SMTP handshake
May 22 17:17:49 emp87 postfix/postscreen[805286]: DISCONNECT
[184.72.250.175]:35556
Interesting... 184.72.250.175 (smtpout37.briteverify.com) connected for
5.2 seconds and did nothing. I suspect that they got tired of waiting
for a banner, since that's less than the default banner delay for
postscreen.
May 22 17:17:50 emp87 postfix/postscreen[805286]: PASS NEW
[107.20.235.139]:41162
May 22 17:17:52 emp87 postfix/smtpd[805371]: connect from
smtpout10.briteverify.com[107.20.235.139]
OK, so THAT host waited long enough to get past postscreen.
May 22 17:17:54 emp87 postfix/smtpd[805371]: NOQUEUE: reject: RCPT
from smtpout10.briteverify.com[107.20.235.139]: 550 5.1.1
<ptzmxjwhaby4gptl062gu9q886spsiiymnz155jrf_y9yy_8k76zw5ge4af55...@simonandkate.net>:
Recipient address rejected: User unknown in virtual alias table;
from=<[email protected]>
to=<ptzmxjwhaby4gptl062gu9q886spsiiymnz155jrf_y9yy_8k76zw5ge4af55...@simonandkate.net>
proto=SMTP helo=<smtpout.briteverify.com>
May 22 17:17:54 emp87 postfix/smtpd[805371]: lost connection after
RCPT from smtpout10.briteverify.com[107.20.235.139]
May 22 17:17:54 emp87 postfix/smtpd[805371]: disconnect from
smtpout10.briteverify.com[107.20.235.139] helo=1 mail=1 rcpt=0/1
commands=2/3
Checking for a random (and exceedingly unlikely) address. Determining
whether your domain has a catchall, i.e. eliminating services like
Mailinator.
May 22 17:17:54 emp87 postfix/postscreen[805286]: CONNECT from
[50.19.110.184]:41342 to [192.168.1.230]:25
May 22 17:17:54 emp87 postfix/dnsblog[805319]: addr 50.19.110.184
listed by domain hostkarma.junkemailfilter.com as 127.0.1.1
May 22 17:17:58 emp87 postfix/postscreen[805286]: CONNECT from
[184.72.250.175]:35616 to [192.168.1.230]:25
May 22 17:17:58 emp87 postfix/dnsblog[805317]: addr 184.72.250.175
listed by domain hostkarma.junkemailfilter.com as 127.0.1.1
May 22 17:18:00 emp87 postfix/postscreen[805286]: PASS OLD
[50.19.110.184]:41342
Apparently you've seen 50.19.110.184 recently. So postscreen lets it
through.
May 22 17:18:01 emp87 postfix/smtpd[805371]: connect from
smtpout29.briteverify.com[50.19.110.184]
May 22 17:18:03 emp87 postfix/postscreen[805286]: HANGUP after 5.2
from [184.72.250.175]:35616 in tests before SMTP handshake
May 22 17:18:03 emp87 postfix/postscreen[805286]: DISCONNECT
[184.72.250.175]:35616
Once again, 184.72.250.175 shows up and stares at you blankly for 5.2
seconds before walking away.
May 22 17:18:03 emp87 policyd-spf[805831]: prepend
Authentication-Results: mail.simonandkate.net; spf=pass (mailfrom)
smtp.mailfrom=origindata.com (client-ip=50.19.110.184;
helo=smtpout.briteverify.com; [email protected];
[email protected])
May 22 17:18:03 emp87 postfix/smtpd[805371]: E32D89606:
client=smtpout29.briteverify.com[50.19.110.184]
May 22 17:18:04 emp87 postfix/smtpd[805371]: disconnect from
smtpout29.briteverify.com[50.19.110.184] helo=1 mail=1 rcpt=1 quit=1
commands=4
Meanwhile, 50.19.110.184 makes it through to a successful RCPT command
for postmaster before politely declining to send email.
...and the webpage pops up an error about it being an invalid email
address. I can use my work email address and it validates and I can
order dinner :-D
"Work" email systems tend to avoid (or not even have support for)
anything that intentionally delays mail.
Has anyone else any experience on what exactly they are looking for to
actually validate? They don't actually appear to test for my email
address, rather the non-valid recipient address which is rejected,
then postmaster which passes early tests but is disconnected by the
client before being fully sent.
My guess is that the 5.2-second null connections are significant. I
suspect that you can fix this without significantly damaging the effect
of the postscreen PREGREET test by reducing the wait time to never
exceed that 5.2 seconds, e.g.:
postconf -e 'postscreen_greet_wait = ${stress?{2}:{4}}s'
That will probably reduce your overall PREGREET rejections by <1% but IF
that is the cause of the null sessions from Briteverify, it should fix
them.
OR: You could complain to the food delivery company that their
disreputable mail verification provider is rejecting valid addresses and
they should save their money by just doing normal verification with a
human component (i.e. email you a code to enter into the form.)
--
Bill Cole
[email protected] or [email protected]
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire
