421 4.7.0 [TSS04] error (Yahoo / AOL): Temporarily deferred for volume or complaints
Yahoo is deferring mail from this IP because of unexpected volume or user complaints. It's a temporary reputation throttle, not a refusal.
How to fix 421 4.7.0 [TSS04]
- Cut the volume and spread the send over more hours; keep retrying through the normal queue.
- Reduce complaints: remove unengaged recipients, make the unsubscribe easy, and match the content to what people signed up for.
Why this happens
Receivers score every sending IP and domain. A history of complaints, spam-trap hits, high bounce rates or a listing on a blocklist pushes that score down until mail is deferred or refused outright.
How to keep it from coming back
Warm up new domains and IPs gradually, send only to verified and relevant recipients, keep complaints near zero, and check your IPs and domains on blocklists regularly. Spread volume across mailboxes and domains instead of pushing one harder.
Should I retry a 421 4.7.0 [TSS04] error?
Normally you don't have to do anything: a temporary error means the receiving server asked for a delay, and your mail server retries on its own for hours or days. Don't resend by hand on top of the queue. If the same deferral keeps coming back from one provider, treat it as a signal to slow down, not as bad luck.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
If these deferrals keep returning, the cause is your volume or reputation. We can find it and sort it out with you.
How we help: Consulting · Private infrastructure · Managed mailboxes · Monthly support