421 4.7.0: try again later (rate limited or temporarily deferred)
The receiving server is asking you to slow down or try again later.
Temporary failure (soft bounce)
What 421 4.7.0 means
A temporary rejection. The server is busy, or thinks you are sending too much or too fast, or is greylisting a sender it has not seen before. A well-behaved sending system retries automatically.
Common causes
- Sending too many messages too quickly
- A new or unwarmed sending domain or IP
- Greylisting
- A temporary server fault
How to fix it
- Let your system retry; most such mail is delivered within hours
- Slow down and spread large sends over time
- Warm up new sending domains gradually
What to do with the address
Do not remove the address. The problem is your sending rate or reputation, not the recipient.
Check an address now with the free email checker, or look at a domain's mail setup with the email domain checker, MX lookup and SPF checker.
Related error codes
Frequently asked questions
- What does 421 4.7.0 mean?
- The receiving server is asking you to slow down or try again later. A temporary rejection. The server is busy, or thinks you are sending too much or too fast, or is greylisting a sender it has not seen before. A well-behaved sending system retries automatically.
- Is 421 4.7.0 a hard bounce or a soft bounce?
- Temporary failure (soft bounce). It may succeed on a later attempt.
- What should I do with the address after 421 4.7.0?
- Do not remove the address. The problem is your sending rate or reputation, not the recipient.