A deferral is a temporary refusal by a mailbox provider or mail server to accept an email message for delivery. The message is temporarily deferred but may be accepted at some point in the future.
There are several reasons your email may be deferred:
- Your IP address has little to no sending history.
- You have incorrect connections or throughput settings.
- Mailbox providers employ graylisting techniques.
- You have exceeded acceptable unknown user rates or complaint rates.