Mail errors · Gmail

What does “421 4.7.28 Gmail has detected an unusual rate of email” mean?

Gmail saw far more mail than usual from your address, domain or server, and slowed it down.

Last read from the sources at the foot of this page.

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Gmail bounce
Mail Delivery Subsystem
421 4.7.28

Gmail has detected an unusual rate of email

As Gmail prints it.
01

What does it mean?

Gmail limits email that arrives at an unusual rate, or an unusual rate of unsolicited email. The wording says what it measured: your IP address, your DKIM domain or your SPF domain.

02

What exactly does the source say?

421 4.7.28 Gmail has detected an unusual rate of email. To protect our users from spam, email has been temporarily rate limited. To review our bulk email senders guidelines, go to Email sender guidelines.

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

Same fix: 421 4.7.28
421 4.7.28 Gmail has detected an unusual rate of email originating from your IP address ip-address. To protect our users from spam, email sent from your IP address has been temporarily rate limited. To review our bulk email senders guidelines, go to Email sender guidelines.
Same fix: 421 4.7.28
421 4.7.28 Gmail has detected an unusual rate of unsolicited email originating from your DKIM domain domain-name. To protect our users from spam, email sent from your domain has been temporarily rate limited. To review our bulk email senders guidelines, go to Email sender guidelines.
Same fix: 421 4.7.28
421 4.7.28 Gmail has detected an unusual rate of unsolicited email originating from your SPF domain domain-name. To protect our users from spam, email sent from your domain has been temporarily rate limited. To review our bulk email senders guidelines, go to Email sender guidelines.
Same fix: 550 5.7.28
550 5.7.28 There is an unusual rate of unsolicited email originating from your IP address. To protect our users from spam, email sent from your IP address has been blocked. To review our bulk email senders guidelines, go to Email sender guidelines.
03

Why would a small firm see it?

A mailbox whose password was stolen and is now sending spam, or a large newsletter sent all at once from ordinary mailboxes.

04

How do I fix it?

  1. Look at the Sent folder of the mailbox that got the bounce.Mail you did not write means the account is being used: change its password and turn on two-step sign-in.
  2. Send newsletters and large mailings through a service built for them, set up with your domain.
  3. Send only to people who asked for your mail.
Sources

Where does this come from?

Related
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