Exchange Online and Paessler PRTG: Monitoring with Modern Authentication

Back in October 2022, Microsoft removed the ability to use Basic authentication in Exchange Online for a wide range of protocols - including Exchange ActiveSync (EAS), POP, IMAP, Remote PowerShell, Exchange Web Services (EWS), Offline Address Book (OAB), and Outlook for Windows and Mac. If you've been working in IT administration for a while, you probably remember the scramble that followed. Suddenly, every app, every script, every monitoring tool that relied on Basic authentication had to be updated. No exceptions.

The bottom line: any app or service that connects to Microsoft Exchange Online now needs to use modern authentication - there's no way around it.

So what does this mean for your PRTG setup? Good news: the Microsoft 365 Mailbox Sensor in PRTG supports modern authentication and is available in all PRTG editions. If you need to monitor Exchange Online mailboxes reliably, this sensor is your answer. It uses the Microsoft Graph API under the hood, which means it fits neatly into today's cloud services landscape - no legacy protocols like SMTP Basic Auth or outdated Exchange Web Services workarounds needed.

The sensor shows you the number of emails in the mailbox, tracks email activity, and gives you the age of the newest and oldest emails. You can also dig into mailbox size data and apply filters to narrow things down. When adding the sensor, you can choose specific folders in the mailbox - or even monitor a shared mailbox by entering the principal user name in the Add Sensor dialog. For helpdesk teams and IT admins alike, that kind of flexibility makes a real difference in day-to-day operations - whether you're running a pure SaaS setup or managing a hybrid environment where an on-premises Exchange Server still acts as your primary mail server alongside Microsoft 365.

How to set up the Microsoft 365 Mailbox Sensor

Before you can start pulling metrics from your Microsoft 365 mailbox, there's some groundwork to do. It's not complicated, but it's important to get it right - especially when it comes to permissions and authentication settings. Here's what the sensor needs:

• Credentials for Microsoft 365 (Tenant ID, Client ID, and Client Secret) must be stored in the settings of a parent object in the PRTG hierarchy. You can obtain these credentials via the Microsoft Azure Portal or the Microsoft Entra admin center.
• The PRTG web server must accept incoming HTTPS requests.
• The sensor requires the correct permissions for Microsoft Graph.
• A redirect URI must be configured in the Microsoft Azure Portal.

One thing worth noting: if your organization uses Azure Active Directory (now Microsoft Entra ID) to manage identities, you're already halfway there - the app registration process ties directly into your existing Active Directory setup. Sounds like a lot? It's manageable, especially with the right docs in front of you. We've put together a step-by-step knowledge base article that walks you through every part of the setup process: How do I obtain credentials and set permissions for the Microsoft 365 Mailbox sensor?

That's your first stop. Read through it, follow the steps, and come back to add the sensor. Once you're ready, the PRTG manual has everything you need for the sensor configuration itself - scroll down to the "Add sensor" section and you're good to go: PRTG Manual: Microsoft 365 Mailbox Sensor

Once the sensor is up and running, it gives you a clear, real-time dashboard view of your Exchange mailbox data. The sensor overview shows you the key metrics at a glance: email count, mailbox size, the age of your oldest and newest messages, and more. You can also filter emails by criteria like "Subject", "From", "Body", or "Age" directly in the sensor settings.

This kind of granular observability is what makes a difference when you're troubleshooting a mail flow issue, investigating email queues that are backing up, or trying to keep track of email activity across your Exchange environments. PRTG also lets you set up notifications so your team is alerted the moment something looks off - no more manual exchange reporting or digging through usage reports to find out what went wrong.

As a monitoring software and application monitoring solution, PRTG is built to optimize your workflow around server monitoring and performance monitoring. Instead of switching between tools, you get all the functionality you need to monitor Exchange Online service health in one place - your PRTG dashboard. That's a real time-saver, especially when Outlook issues or other end-user complaints start piling up and you need answers fast.

And it doesn't stop at email. If your organization runs a broader Microsoft 365 workload - think SharePoint, Microsoft Teams, or Microsoft Office apps - PRTG helps you keep an eye on the full stack. You can also automate alerting workflows so that the right person gets notified at the right time, without anyone having to manually check dashboards. Whether your infrastructure lives on-premises, in the cloud, or spans across multiple environments including AWS, PRTG gives you a unified view. That matters a lot when you're responsible for endpoint health, mobile device connectivity, and compliance requirements like DLP policies - all at the same time.

Try PRTG for free

Still not monitoring your Microsoft 365 mailboxes with PRTG? Start your free 30-day trial today and get full visibility into your Exchange Online service - real-time, no fuss.

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