How to Fix 421 4.7.0 Throttling Errors
Seeing 421 4.7.0 in your logs? It's a temporary throttle, not a permanent block — but ignore it and it gets worse. Here's how to fix it.
TL;DR
421 4.7.0 is a temporary deferral meaning you're sending too fast or your reputation is shaky. Lower rate limits, slow your warmup, and improve reputation. It's recoverable.
What 421 4.7.0 means
The 4 means temporary — the provider is deferring, not rejecting. 4.7.0 indicates a policy/reputation throttle. The provider is saying "slow down, I'm not sure about you yet."
Common causes
- Sending too fast for your current reputation.
- New/cold IP without proper warmup.
- Reputation dip from bounces or complaints.
- Too many connections to one provider.
How to fix it
- Reduce rate limits — lower max-msg-rate and connections per ISP (see throttling guide).
- Respect the deferral — let PowerMTA retry on schedule; don't hammer.
- Check reputation — review IP/domain reputation and fix underlying issues.
- Slow your warmup — if mid-warmup, hold volume for a couple of days.
What not to do
Don't retry aggressively or spin up more connections — that escalates the throttle toward a block. Patience plus lower volume is the cure.
Prevention
Proper warmup, conservative limits and clean lists prevent most 421s. They're a tuning signal, not a disaster.
AutoPMTA auto-tunes throttling and surfaces deferrals so 421s get handled before they escalate. View plans.
Key takeaways
- 421 4.7.0 is a temporary reputation/rate throttle.
- Lower rate limits and connections per ISP.
- Respect the deferral — don't retry aggressively.
- Fix reputation and slow warmup to prevent it.
Frequently asked questions
What does 421 4.7.0 mean?+
It's a temporary SMTP deferral indicating a policy or reputation throttle. The provider is asking you to slow down because your sending rate or reputation isn't yet trusted at that volume.
Is a 421 error permanent?+
No. The leading 4 means it's temporary. The message will be retried, and once you reduce your rate or improve reputation, delivery resumes.
How do I stop getting 421 throttling errors?+
Lower your per-ISP rate limits and connections, respect the deferral instead of retrying aggressively, warm up new IPs properly, and fix any reputation issues from bounces or complaints.