Hi,
some of our users have forwarded the email to Gmail and Gmail now are complaining that this is bulk mail and delaying it.
We have SPF, DKIM, DMARC, even SRS to try these things do not happen 
Anyone know if there is any new policy in Gmail about that?
Above all, the message refers to a non-existent URI!
RSET
250 2.1.5 Flushed v69si8136768yhd.33 - gsmtp
<xxxx@gmail.com>... Using cached ESMTP connection to gmail-smtp-in.l.google.com. via esmtp...
MAIL From:<xxx@example.com> SIZE=150374 BODY=8BITMIME
250 2.1.0 OK v69si8136768yhd.33 - gsmtp
RCPT To:<xxxx@gmail.com>
DATA
250 2.1.5 OK v69si8136768yhd.33 - gsmtp
354 Go ahead v69si8136768yhd.33 - gsmtp
.
421-4.7.0 [163.10.4.2 15] Our system has detected an unusual rate of
421-4.7.0 unsolicited mail originating from your IP address. To protect our
421-4.7.0 users from spam, mail sent from your IP address has been temporarily
421-4.7.0 rate limited. Please visit http://www.google.com/mail/help/bulk_mail.
421 4.7.0 html to review our Bulk Email Senders Guidelines. v69si8136768yhd.33 - gsmtp
QUIT
Eduardo.-
Auto forwarded mail is like that. Any inbound spam your users receive also
gets forwarded. So...
The correct URL should be Email sender guidelines - Google Workspace Admin Help
The URL is actually correct, it just happens that the "html" part in
"bulk_mail.html" only shows up on the next line - if you use it, it
eventually redirects to the above.
Have you double-checked your setup to make sure it is performing SRS correctly? In my experience, Google is secretly blacklisting certain IPs for unknown, unpublished reasons, and implementing SRS seems to be a surefire workaround.
If you aren't on the secret blacklist, mail will still pass even if it fails SPF, but once you are on the blacklist, mail that fails SPF (either softfail or fail) will not be delivered. If a user of yours is forwarding mail from your server to Gmail, the SPF check is not going to be against *your* SPF record, but against the original sender's SPF record, and so the check will fail (since the message looks like it is coming from you, and your MX won't be listed in the original sender's SPF record...thus, it will look like you are spoofing mail for the original sender). Adding a valid SPF record to your domain and then implementing SRS on your mail server should ensure that all SPF checks pass, even for mail that your users are forwarding to Gmail.
I wrote a post detailing my experience and findings: http://www.brokenbitstream.com/gmail-spf-policy