Inbound Mail in a deferred state- 451 4.4.4 Temporary server error. Please try again later ATTR5
| Situation | Your Inbound mail is deferred with a Temporary Server Error |
|---|---|
| Solution | Licensing issues on the O365 side. |
Temporary Server error-451 4.4.4-Please try again later ATTR5
Why are the Inbound messages deferred?
Proofpoint attempts to hand the mail to the O365 server, but the O365 tenant cannot accept messages for this particular domain. The message will appear as " Deferred in the Proofpoint message logs. Typically you will find that the issue is related to a Third Party Vendor that hosts their O365 mail, but I would confirm that with the customer. It's a licensing issue related to the user's mailboxes.
Resolution
The mailbox licenses will need to be set on the O365 side or the Hosted Provider(e.g., Appriver, Intermedia, Rackspace, etc.) before mail flow will resume normally.