554 5.2.0 STOREDRV.Deliver; delivery result banner
The message was accepted by Exchange Online and then failed while being written into the recipient's mailbox. The STOREDRV prefix means the mailbox store driver raised the error; the exception name after it says why. It is a problem inside the recipient's tenant, not with your sending setup.
What the server replies
554 5.2.0 STOREDRV.Deliver.Exception:ObjectNotFoundException.MapiExceptionNotFound; Failed to process message due to a permanent exception with message Cannot open mailbox /o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=DB8PR05MB1234/cn=Microsoft System Attendant [BeginDiagnosticData]...
- Sent by
- Microsoft 365
- Type
- PermanentRetry fails
- About
- Recipient problems
- Enhanced code
- 5.2.0
Who sends it
Exchange Online mailbox servers, after the message has passed transport, when delivery to the mailbox database fails. The sender gets a non-delivery report rather than an SMTP rejection, because the message had already been accepted.
Why it happens
- The mailbox is in the middle of a migration or move and the store cannot open it.
- The mailbox was soft-deleted or is disconnected from its user account.
- A corrupt item or an inbox rule that throws when the message is processed (RuleProcessingException).
- The recipient's mailbox is over its quota in a way that surfaces as a store exception rather than 5.2.2.
How to fix it
Wait and retry once
If the mailbox is being moved, the error clears when the move completes. One retry a few hours later is worth it before escalating.
Send the NDR to the recipient's admin
The diagnostic data in the bounce names the exception and the mailbox database. An Exchange admin can check the mailbox's status in the admin center or with Get-MailboxStatistics.
Admin: repair the mailbox
Reconnect a disconnected mailbox, remove the inbox rule that fails, or run New-MailboxRepairRequest for a corruption exception.
Related codes
- 550 5.4.1 Recipient address rejected: Access deniedExchange Online looked the recipient up in the tenant's directory and did not find it, so it refused the address at RCPT TO.
- 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookupExchange tried to resolve the recipient address against its directory and found nothing.
- 452 4.2.2 Mailbox full / over quotaThe recipient's mailbox has no room for the message.
Sources
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