MC256939 – As announced in MC239262 and on this blog post, Exchange Online is starting to enforce our published mailbox receiving rate limit, incrementally lowering the threshold until reaching the documented limit of 3600 messages per rolling hour.
Microsoft has detected that some tenants have configured their alternate journaling mailbox to point to an address hosted in Exchange Online, which as described in the configuration documentation is an unsupported configuration and due to the new enforcement of limits may cause throttling on alternate Journal mailbox and loss of the Journal Report NDR emails.
Note: If your organization is not using Exchange Online’s journaling functionality you can safely disregard this message.
As a reminder, Microsoft’s best practice to meet your email compliance and regulatory needs is to leverage their Microsoft 365 Compliance suite of solutions rather than journaling messages to another location.
How this will affect your organization:
If your organization is using Exchange Online’s journaling functionality and has configured your alternate journaling mailbox to an address hosted in Exchange Online, due to the updated enforcement of limits, you may lose Journal Report NDR emails sent to your cloud-hosted alternate Journal mailbox if it exceeds the established rate limit.
What you need to do to prepare:
To confirm whether you have this unsupported configuration:
- Go to the “non-delivery reports” email configuration under the Journal Rules section of your classic Exchange Admin Center
- Validate if the selected address is an Exchange Online mailbox
- If you do not have any address selected here or the address selected is not an Exchange Online mailbox, you are not required to take any action.
- If you do have this unsupported configuration, you must update the email address to a mailbox outside of Exchange Online before May 31st to avoid losing NDR emails sent to this mailbox in the event that your primary journaling mailbox becomes unavailable.
If you need more time to update this configuration for your alternate journaling address, please contact Microsoft Support, in certain cases Microsoft may be able to grant up to a 30-day grace period for changes to be made.
Click the Blog link to learn more.