Unsolicited Rate Limit Error - To Gmail

[#1]

Has anyone come across this error reported by Gmail today 30/09/2026.

Reporting-MTA: dns; gateway1.enmail.co
X-Postfix-Queue-ID: ECB3F46454
X-Postfix-Sender: rfc822; {my email address .....plus.com}
Arrival-Date: Wed, 30 Sep 2026 08:18:25 +0000 (UTC)

Final-Recipient: rfc822;  {sending to gmail address}

Original-Recipient: rfc822;  {sending to gmail address}
Action: failed
Status: 4.7.28
Remote-MTA: dns; alt1.gmail-smtp-in.l.google.com
Diagnostic-Code: smtp; 421-4.7.28 Gmail has detected an unusual rate of mail
    originating from your SPF 421-4.7.28 domain [<xxxxx>.plus.com      35].
    To protect our users from 421-4.7.28 spam, mail sent from your domain has
    been temporarily rate limited. 421-4.7.28 For more information, go to
    421-4.7.28  https://support.google.com/mail/?p=UnsolicitedRateLimitError to
    421 4.7.28 review our Bulk Email Senders Guidelines.
    4fb4d7f45d1cf-6ae16d50391si1239068a12.208 - gsmtp

Three separate emails all bounced....

[#2]

This is a question to raise with Greenby.

@plusnettony FYI - does this look like Gmail is already getting snotty with the Greenby gateway subsequent to the migration of relay.plus.net to their proxy?

[#3]

Possibly, it looks to be checking plus.com again as one email address (If I'm reading it correctly).

I've sent a test message, and I'm just waiting for a bounce. 

[#4]

Possibly, it looks to be checking plus.com again as one email address (If I'm reading it correctly).

I can understand(to some extent!) why it did that previously when DKIM was implemented as 'relaxed' on the plus.com domain. However from looking at a test email sent yesterday, both DKIM & SPF are implemented on the <account>.plus.com subdomain, so what earthly reasoning does gmail have for treating everything as coming from the parent domain? 

but I guess gmail will do whatever they want to...

[#5]

Wait for Microsoft to re-adopt the same tactics...

[#6]

to answer my own question...

I guess where the parent domain is NOT a TLD , gmail are trying to preclude the trick of using subdomains to get around their rate limiting for a domain.

[#7]

I'm usually the very opposite of a Conspiracy Theorist but...

There has to be some 'rational'(?) explanation for this behaviour. I have noted comments online that this might be construed as a tactic by both Gmail and Microsoft to completely take over the email business. Perhaps it is time for it to be looked into closely at an official level?

[#8]

That idea was mentioned in the earlier 'discussions' on this subject, @pvmb .

[#9]

From: https://support.google.com/mail/answer/81126?visit_id=639264466974178337-3459158831&p=UnsolicitedRat... 

Is: 

Starting February 1, 2024, email senders who send more than 5,000 messages per day to Gmail accounts must meet the requirements in this section.

• Set up SPF and DKIM email authentication for your domain.
• Set up DMARC email authentication for your sending domain. Your DMARC enforcement policy can be set to none.

relevant? Specifically, does Greenby add a DMARC record?

[#10]

relevant? Specifically, does Greenby add a DMARC record?

An <account>.plus.com domain is unlikely to send >5000 messages / day, so it shouldnt apply.

However AFAICS there IS a DMARC record defined for each <account>.plus.com domain.

For info, a test message I sent earlier this morning to a gmail address WAS delivered but marked as Spam.

[#11]

My test came through as expected albeit delayed. I'll look at some other tests. 

[#12]

@MisterW / @Baldrick1 

I just ran a MXToolBox query on my account.plus.com domain...

• There is no sub-domain DMARC record
• There is a DMARC record for plus.com
• That is reported by PlusNet's DNS service

I have attempted to configure a sub-domain (hosted domain) DMARC record in the Greenby portal following the AI support instructions.  The UI does not permit "_dmarc" as a host name.  I have an open fault report on the matter.

So from a validation point of view, DMARC remains unaltered.

What does perplex me is that MXToolBox is indicating that the queries are coming from PLUSNET's NS, not Greenby's.  A nslookup of the domain reports the NS as "primary name server = ns1.force9.net".

There is DKIM on the subdomain - the MXToolBox query advises that was reported by Greenby's DNS.

[#13]

@Townman 

For my <account>.plus.com domain MXtoolbox says there IS a DMARC record

Odd though, mine reports the NS as ns1.plusnet.co.uk ?

[#14]

@MisterW 

Could this possibly be residual from your account being used as a lab-rat for testing email domain verification options a few years back.  Remember you had SPF when others did not.

[#15]

I was just thinking that...