What does “421 4.7.40 Your email has been rate limited because the sending domain doesn't have a DMARC record” mean?

What does it mean?

Gmail requires a DMARC record from domains that send more than 5,000 messages a day to Gmail accounts. 421 is a temporary limit; 550 5.7.40 is a block.

Without a DMARC record, nothing tells mail servers to refuse mail forged in your name.

What exactly does the source say?

421 4.7.40 Your email has been rate limited because the sending domain doesn't have a DMARC record, or the DMARC record doesn't specify a DMARC policy. Gmail requires all bulk email senders to add a DMARC record to their sending domain. See Set up DMARC. To learn more about Gmail requirements for bulk email senders, visit Email sender guidelines.

Gmail's page writes domain-name and ip-address where your bounce shows your own domain and the sending address.

550 5.7.40 Your message was blocked because the sending domain doesn't have a DMARC record or the DMARC record doesn't specify a DMARC policy. Gmail requires all bulk email senders to add a DMARC record to their sending domain. See Set up DMARC. To learn more about Gmail requirements for bulk email senders, visit Email sender guidelines.

Why would a small firm see it?

The domain never had a DMARC record, or the record is there but has no p= tag. A newsletter sent to a large list in your name can pass the 5,000 mark.

How do I fix it?

1. Start herep=nonereports only
2. p=quarantinesuspicious mail to spam
3. Where to aimp=rejectforged mail refused

v=DMARC1; p=none; rua=mailto:[email protected]

v=DMARC1; p=quarantine; rua=mailto:[email protected]

v=DMARC1; p=reject; rua=mailto:[email protected]

1. Publish one TXT record named _dmarc with the p=none value shown here.Use a mailbox someone reads for the reports.
2. Read the reports for a few weeks.Each row names an address that sent mail as your domain and whether it passed.
3. When every service you use passes, move to p=quarantine, then to p=reject.

Use your own domain and a mailbox someone reads where the record shows yourfirm.example.

What else do the sources say?

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.