Ceyhun KIRMIZITAS

02Sep 2026 by Ceyhun Kirmizitas 0 Comments

Exchange Server SE / 2019 OWA Authentication Deep Dive – Part 2: Forms-Based and Basic Authentication – What Really Changes?

Exchange, Exchange Server SE / 2019 / 2016

Applies to: Exchange Server SE / 2019 / 2016 Summary: In Part 1, we mapped the OWA authentication layers and captured the default configuration. In this part, we change only the frontend OWA authentication settings and watch what happens in Exchange, IIS, and the browser. Changing one Exchange OWA authentication setting can completely change what IIS allows and what the browser shows. Understanding those differences makes it much easier to tell a real authentication failure from an expected 401 challenge, a Basic prompt, or the normal Exchange OWA sign-in flow. Part 1: How OWA Authentication Really WorksPart 2: Forms-Based and Basic Authentication – What Really Changes? — you are herePart 3: Frontend vs Backend Authentication – Controlled A/B TestsPart 4: Troubleshooting OWA Authentication with IIS and HttpProxy LogsPart 5: Managed…

31Aug 2026 by Ceyhun Kirmizitas 0 Comments

Exchange Server SE / 2019 OWA Authentication Deep Dive – Part 1: How OWA Authentication Really Works

Exchange, Exchange Server SE / 2019 / 2016

Applies to: Exchange Server SE / 2019 / 2016 Summary: OWA authentication is easier to troubleshoot once the frontend, Exchange authentication layer, HttpProxy, and backend are treated as separate parts of the same request. This first part sets the baseline, shows the main commands, and explains which settings matter before we start changing anything. Exchange OWA authentication problems are easy to misdiagnose because the browser, frontend IIS, Exchange authentication layer, HttpProxy, and backend do not tell the same story. Before changing any setting, you need to know which layer actually owns the failure. Version scope: The controlled tests in this series were performed on Exchange Server 2019 CU15 and Exchange Server Subscription Edition (SE) RTM. Microsoft states that SE RTM is code-equivalent to Exchange 2019 CU15 apart from the license…

25Aug 2026 by Ceyhun Kirmizitas 2 Comments

Get Exchange Server URLs and Authentication Settings with PowerShell

Exchange, Exchange Server SE / 2019 / 2016

Applies to: Exchange Server SE / 2019 / 2016 The original GetExchangeURLs.ps1 script was written by Paul Cunningham to provide a simple way to display Exchange Server Client Access URLs from a single PowerShell script. Ali Tajran later updated the script to version 1.10, adding the PowerShell virtual directory and reorganizing the output. I recently revisited the script and decided to continue the same approach rather than create a completely new one. The result is GetExchangeURLs-v2.ps1. Download GetExchangeURLs-v2.ps1 Download from GitHub Questions and feedback are welcome in the comments below. For script issues or feature requests, please use GitHub Issues. Current version: 2.2 (October 9, 2026). See What Changed below for the version history. In This Article 1. What Changed 2. Get Exchange Server URLs 3. Alternate Service Account (ASA)…

24Aug 2026 by Ceyhun Kirmizitas 0 Comments

Get-ExchangeCertificate Returns Blank with a Valid Auth Certificate

Exchange, Exchange Server SE / 2019 / 2016

Applies to: Exchange Server 2019 CU15 While validating a fresh Exchange Server 2019 CU15 installation, I started capturing the default configuration before making any namespace, certificate, or authentication changes. One of the first checks was Get-ExchangeCertificate. Unexpectedly, the cmdlet returned only the column headers and no certificate objects, even though the Exchange Admin Center showed the certificates normally. PowerShellGet-ExchangeCertificateGet-ExchangeCertificate Thumbprint Services Subject ---------- -------- ------- At first, this looked like the known Exchange Auth Certificate issue associated with PowerShell Serialization Payload Signing. However, the Auth Certificate was present, valid, correctly configured, and Microsoft's validation script reported no problem. What initially looked like a certificate problem eventually turned out to be related to the timing of certificate activation and HMAC key selection. In This Article 1. Certificates Were Present and the…

22Aug 2026 by Ceyhun Kirmizitas 0 Comments

Troubleshooting Microsoft Entra Pass-through Authentication in Multi-Forest Environments

Hybrid Identity, Identity, Microsoft Entra ID

Applies to: Microsoft Entra ID | Microsoft Entra Connect Pass-through Authentication | Multi-Forest Active Directory Microsoft Entra Pass-through Authentication (PTA) allows users to sign in to Microsoft Entra ID using passwords that are validated directly against on-premises Active Directory. In a single Active Directory forest, this password validation path is usually straightforward. In a multi-forest environment, however, the PTA agent may need to validate users located in another forest through an Active Directory forest trust. In this scenario, the PTA agent itself can be healthy and successfully validate users in one forest, while Microsoft Entra sign-ins for users in another forest fail through the same agent. In this article, we will look at how Forest Trust and Name Suffix Routing can affect cross-forest password validation with Microsoft Entra Pass-through Authentication.…

12Jun 2026 by Ceyhun Kirmizitas 0 Comments

Handling External Disclaimer Exceptions for Trusted Application Relays in Exchange Hybrid

Exchange, Exchange Online, Exchange Server SE / 2019 / 2016, Hybrid, Security & Hardening

Applies to: Exchange Server SE / 2019 / 2016 | Exchange Online | Hybrid In Exchange Hybrid environments, it is common to use mail flow rules to add an external disclaimer or warning banner to messages received from outside the organization. A typical warning may look like this: WARNING: This email originated from outside the organization. Do not click links or open attachments unless you recognize the sender. This is a good security control. It helps users identify messages that came from external sources. However, there are some scenarios where messages generated by internal application servers may also receive this external disclaimer. This usually happens when an internal application server submits email anonymously to Exchange Server on-premises, and Exchange then routes the message to Exchange Online. In this article, we…

21May 2026 by Ceyhun Kirmizitas 0 Comments

Force OWA Light Users to Premium OWA After Exchange Server May 2026 CVE Mitigation

Exchange, Exchange Server SE / 2019 / 2016, Migration & Upgrade, Security & Hardening

Applies to: Exchange Server SE / 2019 Microsoft recently published guidance for Exchange Server addressing the May 2026 vulnerability. One important note in the article is related to OWA Light. Microsoft states that OWA Light — accessed by using an OWA URL ending with /?layout=light — does not work properly after the mitigation is applied. Microsoft also notes that this feature was deprecated several years ago and is not intended for regular production use. For a deeper look at the OWA request path and frontend/backend authentication design, see Exchange OWA Authentication Deep Dive – Part 1. This can become a practical issue if some users previously selected the following option in Outlook on the web: "Use the light version of Outlook" When this option is selected, the user may continue…

18Mar 2026 by Ceyhun Kirmizitas 0 Comments

What Happens to Shared Calendars After Exchange Hybrid Migration?

Exchange, Exchange Online, Hybrid, Migration & Upgrade

Applies to: Exchange Server SE / 2019 / 2016 | Exchange Online | Hybrid In Exchange Hybrid environments, shared calendar behavior after mailbox migration is often misunderstood. Calendar access does not automatically fail when a mailbox moves to Exchange Online, but the result depends on the permission type, how it was assigned, and the hybrid configuration. This article walks through a controlled test and shows the behavior observed before and after the move. In This Article 1. Scenario 2. Step 1 – Test Default Behavior (On-Prem → On-Prem) 3. Step 2 – Check Existing Permissions 4. Step 3 – Assign Explicit Permission 5. Step 4 – Verify Access 6. Step 5 – Migrate Mailbox to Exchange Online 7. Step 6 – Test After Migration (Both Directions) 7.1 Test 1 –…

15Mar 2026 by Ceyhun Kirmizitas 0 Comments

Reclaiming Space from Inflated Thin VMDK Disks After VM Export in ESXi

VMware, vSphere

Applies to: VMware ESXi 9.x / 8.x / 7.x / 6.7 / 6.5 / 6.0 / 5.5 / 5.1 / 5.0 / 4.1 After exporting several virtual machines from my ESXi environment, I noticed that datastore usage had increased significantly. Although the guest operating systems were using only a small portion of their virtual disks, the VMDK files appeared to occupy space close to their full provisioned size. For example, a virtual machine with a 100 GB thin-provisioned disk that was actually using only around 17 GB inside the guest OS appeared to consume almost the entire provisioned disk size on the datastore. This situation can quickly become problematic in environments where multiple virtual machines are exported or stored for later use. Datastores may appear nearly full even though the…