A risky verdict means the receiving server gave us reason to believe the mailbox exists, but with a signal that sending might not go smoothly. It is deliberately separate from undeliverable: deleting every risky address throws away real subscribers, and blasting all of them at once risks bounces.
What triggers it
- Mailbox full — the account exists but is over quota right now; often temporary.
- Greylisting — the server deliberately delays first-time connections. We retry and wait; when the answer arrives late but positive, the address resolves as risky rather than a clean deliverable.
- Soft rejections and throttling — the server answered evasively or slowed us down instead of giving a clean yes.
What to do with risky addresses
Do not blanket-delete them. Send to risky segments in smaller, spaced batches, watch the bounce rate, and let engagement decide: an address that opens is proven; one that hard-bounces removes itself. If your sender reputation is fragile, hold risky addresses until your deliverable segment has warmed your domain.
Fairness note: when a greylisted check resolves without a definitive mailbox confirmation, we do not pretend to more certainty than we have — and checks that never got a real answer are refunded as unknown.