Unable to email anyone from my primary domain name; thanks Google Mail and G Suite.

Thu Oct 24 00:18:46 UTC 2019

Dear NANOG@,

I'm not sure where else to post this, and this is not really new, either,
but I think I have a new take here.

I use my own personal domain name for various UNIX stuff, including sending
log-related things to myself out of cron, which end up in my own Gmail.com
account, either directly, or through forwarding (w/o SRS).  (I do not use G
Suite for my own domain name, for obvious reasons; just the consumer-based
gmail.com email address from the old times of invitation-based
registrations.)

Over the years, I sometimes had certain messages rejected by Gmail, but it
was a very low rate of rejection (less than 5% for any mail I cared about),
and wasn't a major problem (usually only some automated messages would be
rejected).

A couple of months ago, I setup some new scripts that would send me new
nightly emails.  It's all plain text, but had a few dozen of domain names
present (it's logs).  Absolutely no links, just plenty of domains which I
don't control.  So, Gmail has been presenting most of these messages with
their red warning label that the email contains malicious links, even
though all of these emails contained zero links, zero URLs to any of these
unknown domain names, zero URL schemes, zero "http://", zero "https://"
etc.  You get the idea.

Since about a few weeks ago, I am now seeing at least a 95% rejection rate
for my domain name, for ALL email, including the forwards.  Including
emails which I send to myself from within Google, and which get forwarded
back to Gmail by my UNIX machine (which is not known to break Gmail's DKIM,
either, although it's also difficult to test, because when it does get
through, it's automatically marked as a duplicate by Gmail, so, you don't
get DKIM status from Gmail by looking at the headers, since you only get to
examine the original copy that was sent, not the forwarded duplicate that
was subsequently accepted).  I.e., emails with a passing DMARC still get
rejected.

The funny thing is, Google doesn't actually blacklist my primary IPv6
address in my own /48 from which all of my messages originate; even though
the rDNS resolves to a subdomain on the very same domain name which they've
blacklisted "due to the very low reputation".  They've blacklisted just the
main domain name that I use for my own non-Gmail-hosted mail.  Sending the
same messages into my Gmail.com from a different domain name in MAIL FROM,
which is served from the same zone file DNS-wise (e.g., an SPF pass),
through sendmail's `-f` option, or with Mutt, makes the messages go through
(even with rDNS being "low reputation"); sending it from my primary domain
name in MAIL FROM results in the following:

>>> DATA
<<< 550-5.7.1 [2001:470:xxxx::      19] Our system has detected that this
message is
<<< 550-5.7.1 likely suspicious due to the very low reputation of the
sending
<<< 550-5.7.1 domain. To best protect our users from spam, the message has
been
<<< 550-5.7.1 blocked. Please visit
<<< 550 5.7.1  https://support.google.com/mail/answer/188131 for more
information. 135si403977wma.43 - gsmtp
554 5.0.0 Service unavailable

The support article suggests using Postmaster Tools; great, never heard of
it, sounds cool; let's verify our domain, and try it out, hopefully,
there's a solution right there.

However, after verifying my domain name through DNS for Postmaster Tools,
it is revealed that Postmaster Tools cannot tell me anything at all, with
all tabs and screens being 100% blank, allegedly because I'm not actually a
mass email sender (I don't send hundreds of emails a day or whatnot), and
they're too afraid that I'll figure out why my mail doesn't actually go
through, instead of signing up for G Suite.

Right now, I've had a business need to reply to a work-related email from
some other business.

This is what I got after sending my reply from my primary domain name
through mutt — a nice double rejection by both the G Suite and Gmail in a
single bounce generated by my server:

   ----- Transcript of session follows -----
... while talking to aspmx.l.google.com.:
>>> DATA
<<< 550-5.7.1 [2001:470:xxxx::      19] Our system has detected that this
message is
<<< 550-5.7.1 likely suspicious due to the very low reputation of the
sending
<<< 550-5.7.1 domain. To best protect our users from spam, the message has
been
<<< 550-5.7.1 blocked. Please visit
<<< 550 5.7.1  https://support.google.com/mail/answer/188131 for more
information. z11si12494671wrw.137 - gsmtp
554 5.0.0 Service unavailable
... while talking to gmail-smtp-in.l.google.com.:
>>> DATA
<<< 550-5.7.1 [2001:470:xxxx::      19] Our system has detected that this
message is
<<< 550-5.7.1 likely suspicious due to the very low reputation of the
sending
<<< 550-5.7.1 domain. To best protect our users from spam, the message has
been
<<< 550-5.7.1 blocked. Please visit
<<< 550 5.7.1  https://support.google.com/mail/answer/188131 for more
information. 135si403977wma.43 - gsmtp
554 5.0.0 Service unavailable

Changing MAIL FROM into a non-primary domain name (served out of an
identical zone file, basically) gets the message accepted, without DKIM,
without the 4-minute delay that many "suspicious" messages have had for
months now, from the very same IPv6 address with the rDNS pointing to the
domain name with "the very low reputation", and it shows up in both my own
Gmail as well as, presumably, in the G Suite account of the business
partner I was replying to.  (Note that this trick where the rDNS domain
gets ignored works only for new emails with a passing SPF; I presume the
rDNS still prevails in bringing the "low reputation of the sending domain"
for forwards, as they don't seem to succeed any longer now.)

There are a number of possible tl;dr: takeaways here:

* don't spread the monoculture — don't use G Suite for your organisation;

* don't send crontab output to your Gmail from your primary domain name;

* don't use Gmail.

What is my own takeaway here?

* Without being an anti-Google zealot, from a purely practical perspective,
since my Gmail account no longer contains the mail I care most about, as it
gets rejected on the SMTP layer, I'll have fewer reasons to use it.

* I'll now have no other choice but to modify my setup to stop forwarding
to Gmail, because my business contacts don't need to see all these bounces
that are now taking place.

* Since so many businesses are G Suite useds, I'm still looking for a
solution to get rid of the "the very low reputation of the sending domain"
from a domain name I've been using since 2007, and which I'm 100% convinced
was blacklisted by Google entirely for me sending crontab with system logs
(zero HTML, zero URLs) to my own Gmail.  I have SPF and DMARC all setup and
passing since years ago, which doesn't stop this issue from occurring.
Merely switching the name of the domain in From and MAIL FROM to any other
domain I own (which points to the very same MX) appears to be my workaround
for now.

Some possible suggestions for Google, if I may:

* Maybe don't convert schemeless domain names which are non-URLs into
"malicious" URLs?  (They already do seem to block them from being presented
as links in the UI in such an instance, but there's little reason for
trying to convert these domain names into links in the first place.)

* Maybe don't consider harmless plain text emails with a bunch of domain
names to contain malicious links when they don't?

* Maybe don't assume everyone with a domain name runs a G Suite?  (Their
whole troubleshooting guide is built around it.)

* Maybe don't assume everyone with a domain name sends hundreds of emails
from their domain name per day?  (They seem to limit Postmaster Tools based
on such a criterion.)

* Maybe don't blacklist a domain name for sending harmless logs to a Gmail
account that lists said domain name as an alternative From address?

Cheers,
Constantine.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.nanog.org/pipermail/nanog/attachments/20191023/b1aa0362/attachment.html>