Your Backup Radar mailbox is hosted in Microsoft 365 (Exchange Online), which enforces receiving limits that can affect how Backup Radar ingests email-based backup results.

If your mailbox exceeds these limits, Microsoft may reject incoming emails. This can result in bounced messages and missing backup results in Backup Radar.

This article explains the receiving limits, how to identify when they may be affecting your mailbox, and what you can do to stay within them.

⚠️ This article references third-party limits and behaviours that may change. For the latest details, see Microsoft's documentation on Exchange Online limits.

Exchange Online receiving limits

Exchange Online enforces the following receiving limits per mailbox:

These limits apply to any mailbox hosted in Exchange Online, including shared mailboxes and distribution groups. The limits reset every hour.

How these limits affect Backup Radar

If you use an email-based integration to send backup results to Backup Radar, the emails are delivered to a mailbox hosted in Microsoft 365.

When the receiving limits are exceeded, Microsoft rejects additional incoming emails before Backup Radar can process them. This can cause the following symptoms:

• Backup results do not appear in Backup Radar.

• Devices display a No Result status on the Audit and Daily Activity pages for periods when results were expected.

• You receive Undeliverable bounce-back messages in the sending mailbox. These messages can further increase email volume and compound the problem.

Common causes

You are most likely to hit these limits when a large number of emails are sent to your Backup Radar mailbox in a short period of time.

Common scenarios include:

• A backup vendor sends a high volume of notification emails, such as error, security, or informational alerts in addition to backup results.

• Multiple backup products route emails to the same mailbox at the same time.

• A backup appliance is misconfigured and sends duplicate or repeated notifications for the same device.

What to do if you suspect you are reaching the limits

Check for bounce-back emails

The clearest sign that you are hitting receiving limits is an Undeliverable bounce-back email from Microsoft 365 indicating that the mailbox has reached its limit. Check the sending mailbox for these messages.

Check your email volume in Backup Radar

1. Go to Integrations > Mailboxes.

2. Open the mailbox in question.

3. Check the number of emails received in the last minute.

If you see approximately 20 or more emails received in the last minute, the mailbox may be approaching its receiving limits.

Reduce unnecessary email notifications

Configure your backup vendor or vendors to send only the notifications that Backup Radar needs to process. Disabling non-essential alerts, such as informational or security notifications that do not contain backup results, can significantly reduce email volume.

Distribute email across multiple senders

If possible, configure your backup notifications to originate from different sender addresses. This helps you stay within the per-sender limit of 1,188 emails per hour.

Once you reduce the email volume below the receiving limits, BackupRadar resumes processing incoming backup results as expected. Because the limits reset hourly, results typically begin appearing again within the next hour.