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Email error 421 4.7.0: Try again later (rate limited or temporarily deferred)

The server is asking you to slow down or come back later. The message is not rejected, it is delayed, and a correctly configured sender retries on its own.

Temporary failure (soft bounce)

What it means

The server is asking you to slow down or come back later. The message is not rejected, it is delayed, and a correctly configured sender retries on its own.

Common causes

  • You sent too many messages to that provider in a short time.
  • The provider sees unusual traffic from your IP and limits it.
  • The server is busy or under maintenance.
  • Your sending reputation is low or new.

How to fix it

  1. Let the mail system retry; do not resend manually in a flood.
  2. Lower your sending speed and spread large campaigns over several hours.
  3. Warm up new domains and IPs gradually.
  4. Clean the list so fewer bounces and complaints lower your reputation.

How to prevent it

Most bounces come from addresses that were never checked. Verify each address before you send: syntax, domain, mailbox and risk are checked without sending a message. Test a single address with the free email checker or upload a whole list for bulk verification.

Verify an email address free · Clean a whole list · MX lookup · SPF, DKIM and DMARC checker

Frequently asked questions

Will the message be delivered?

Usually yes, if the sender keeps retrying according to its schedule.

How long does it last?

Minutes to a few hours, depending on the provider and your reputation.

Other error codes

550 5.1.1User unknown (mailbox does not exist) 550 5.7.1Message rejected by policy (blocked) 550 5.7.26Sender not authenticated (SPF/DKIM/DMARC) 550 5.4.1Recipient address rejected: access denied 552 5.2.2Mailbox full (over quota) 553 5.1.3Invalid address syntax

All email error codes