Definition
Deferred delivery (sometimes called greylisting or a soft deferral) happens when a receiving mail server temporarily refuses a message with a "try again later" response instead of accepting or permanently rejecting it. The sender's system retries after a delay, and if the message is legitimate the later attempt usually succeeds.
Unlike a rejection, a deferral is not a permanent failure. It is a temporary holding action, often used to slow down suspicious bulk senders, manage load, or verify the sending server.
Deferral vs Rejection
| Factor | Deferred Delivery | Rejection |
|---|---|---|
| Server response | Temporary (try later) | Permanent refusal |
| Retry | Happens automatically later | No automatic retry assumed |
| Outcome | Usually eventually delivered | Bounced |
| Meaning | A delay, not a failure | A hard refusal |
A deferral delays delivery; a rejection ends it.
Why Servers Defer Mail
- Greylisting: The server requires the sender to retry before accepting.
- Load balancing: The receiving system is busy and queues the request.
- Rate control: Senders exceeding thresholds are asked to slow down.
- Reputation checks: The server verifies the sender before deciding.
How to Handle Deferred Delivery
- Retry automatically: Configure the sending system to retry deferred messages after the indicated delay.
- Respect retry timing: Delaying the retry often clears the deferral as required.
- Monitor deferral rates: Rising deferrals can signal rate or reputation problems.
- Review delivery status: Not all annex responses appear in normal reporting.
Related Glossary Terms
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
Email Authentication Protocols
Email authentication protocols are technical standards that verify the identity of an email sender, helping mailbox providers distinguish legitimate mail from spam and phishing.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Management
Bounce management is the process of handling emails that are rejected by mailbox providers, including classification, removal of bad addresses and protection of sender reputation.
Frequently Asked Questions
Deferred delivery is when a receiving server temporarily holds a message with a "try later" response rather than accepting or rejecting it. The sender retries and the message is usually delivered on a later attempt.
No. A deferral is temporary — the server asks you to try again and the mail is often accepted on retry. A bounce is a permanent failure where the message is refused and returned.
Deferrals commonly stem from greylisting, receiving-server load, sender rate limits, or reputation checks. Each causes the server to hold the message and request a retry rather than accept it immediately.
Ensure your sending platform retries deferred messages with correct timing, keep sending rates within limits, and maintain a healthy sender reputation. Monitoring deferral rates helps you spot rate or reputation issues early.