A temporary refusal. The receiver is slowing you down — often because of reputation, unusual volume, or missing authentication. Your server will retry automatically.
Soft bounce · temporary
Common causes
- Sending too much too fast from a new IP or domain
- Low or unknown sender reputation
- Missing reverse DNS or authentication (Gmail often defers before rejecting)
- Spam complaints from recent campaigns
How to fix it
- Lower your sending rate and warm up new IPs and domains gradually
- Make sure SPF, DKIM, DMARC and reverse DNS are in place
- Remove unengaged recipients and invalid addresses
Domain CheckerRun the right check for your domain or paste the full bounce message for a precise explanation.
Open Domain Checker →Frequently asked questions
Will 421 messages be delivered eventually?
Usually yes — your server retries. If deferrals continue for days, the message bounces with a delivery-time-expired error.