After sending an email, you may receive a delayed delivery warning. Its exact wording depends on the server; here is an example:
Warning: message still undelivered "Deferred - Delayed -
Warning: message still undelivered after 4 hours, Will keep trying until message is 3 days old"
In short: this is not a failure yet: our server has not yet managed to deliver the message and keeps trying for the time stated in the warning. Wait, check the recipient's address and let them know by another means.
What does this warning mean?
Our mail server attempted to connect to your recipient's mail server to deliver the message, but has not succeeded yet. This is not a failure yet: our server keeps trying to send your message for a certain time, whose length is stated in the warning.
If, after this period, the message has still not been delivered, you will receive a final error message stating that your message could not be delivered and that your recipient did not receive it.
The most common causes are on the recipient's side:
- their mail server is unavailable or overloaded;
- their server temporarily refuses messages from an unknown sender (greylisting);
- the DNS of their domain does not answer correctly.
What should I do?
- Wait: in most cases, the message is eventually delivered without you having to do anything.
- Check the recipient's address, especially the spelling of the domain name.
- Let your recipient know by another means: the problem is most often on their side or with their provider.
- If you receive the final failure notice, send it to support together with the information useful for the diagnosis.
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