Email Routing problem to Gmail

I am (/was) forwarding from Cloudflare to a Gmail account and in the dashboard saw a number of rejects from Google servers which have blacklisted the Cloudflare IP.

The dashboard error is: Unknown error: transient error (421): 4.7.28 [ 15] Our system has detected an unusual rate of\n4.7.28 unsolicited mail originating from your IP address. To protect our\n4.7.28 users from spam, mail sent from your IP address has been tempor…

I had that same notification from a number of different CF IPs (,,,,,,,,, 15,, I’m assuming the service tried to resent the email from a different IP to get deliverability.

Surely unless CF implements spam filtering this is going to be a problem, as CF essential forwards all mails to Gmail (or wherever) even if they’re spammy, then Gmail picks up on this and decides the sending IP can’t be trusted … which means legitimate mails are blackholed.

Just wanted to check how this was being managed, if perhaps I was unlucky, or if this is just to be expected with a large-scale forwarding service.


I am sorry, I don’t have an answer, but I have a similar issue. Email forwarding to gmail does not work at all. Email forwarding to yahoo works, but the emails land in the spam folder.
What I would be interested (since I am a beginner) is how you investigate the issue. Where do you find out that Google servers blacklist the Cloudflare IPs and where do you get the Cloudflare IPs from?
Thank you in advance! Sorry if I bother you.

I got the information from the logs in the Cloudflare dashboard. If you’re not seeing your emails land in Gmail then that’s the place to look if they were sent (forwarded) or dropped or if there was an error.

If they are leaving Cloudflare and not arriving at Google then you could set up DMARC which will give you reports from providers which will give you a little more information about how they’ve treated your mail.

Adding a DNS record such as this:

TXT _dmarc v=DMARC1; p=none; ruf=mailto:[email protected]

will give you a daily aggregate report. It’s hard to understand (it’s in XML format) but there are inline tools you can upload it to which will provide at least some visibility into if your message is being rejected by Google and why.

Personally most of my mail hit Gmail without any issues. There were only a few cases where it seemed to hit this spam wall. I’ve moved all my MX records back to Google for now so the emails are no longer being forwarded by CF as I just met silence on this issue.

Ok, thank you very much for the tips!

Same problem here. A lot of delivery failed messages (including dmarc reports).

i am also getting this error
please help me dear team

Does anyone have a solution?
I am getting the same problem…
Thanks in advance for your answer!