How to fix delivery delays
What to do when receiving servers delay more than 10% of sent mail across consecutive windows.
You got Sustained delivery delays are above 10% of sent mail. Receiving servers accepted the message later (or greylisted / deferred it). This measures delivery delay, not inbox vs spam.
What to change
Delays usually mean the far side is throttling you or retrying. Check, in order:
- Volume spike — a sudden list blast after quiet weeks. Slow the send; don’t retry the same delayed cohort immediately.
- List quality — high bounces/complaints in the same windows. Fix those first (bounce, complaints).
- Authentication — open domain alerts on Settings → Deliverability. Failed DKIM/SPF/DMARC makes deferrals more likely.
- Content — run the content checker on the campaign that was in-flight.
- Dedicated IP warmup — if you use a dedicated IP, see How to fix a dedicated IP.
You cannot force Gmail or Microsoft to stop greylisting. You can stop looking like a bursty or unauthenticated sender.
After it recovers
The alert resolves when consecutive adequate windows stay below 10% delayed / sent.