Microsoft 365 / Exchange
Exchange Online, connectors, mail routing, and hybrid scenarios.
compauth in Microsoft 365: Composite Authentication and All Reason Codes
Microsoft 365 supplements SPF, DKIM, and DMARC with its own evaluation: compauth. What Composite Authentication checks, what pass, softpass, fail, and none mean, and what causes each reason code, from 000 to 905.
AuthMechanism 10 and AuthAs Internal: How Exchange Classifies Message Submission in the Header
The X-MS-Exchange-Organization-AuthMechanism header documents how a submitting server authenticated. Value 10 indicates a Receive Connector with Externally Secured and classifies external emails as internal, with consequences for spam filters, mail flow rules, and spoofing protection.
Internal or External? Interpreting Exchange Hybrid Mail Headers: AuthAs, MessageDirectionality, and X-originatororg
In Exchange hybrid environments, header classification determines whether an email is treated as internal. Which headers carry the classification, how tenant attribution works through certificates and connectors, and how to identify a misrouted message.
VPN Split Tunneling for Microsoft Teams: Routing Media Traffic Around the Tunnel
Teams calls over a VPN suffer from latency, jitter, and the detour through the VPN gateway. This article explains which Microsoft networks and ports handle media traffic, why IP-based split tunneling is superior to app exclusions, and how to implement it in consumer VPNs, WireGuard, OpenVPN, and enterprise clients.
Analyzing Exchange Mail Flow: Message Tracking, SMTP Logs, and Receive Connectors
How to systematically determine where a message ended up in Exchange On-Premises, Hybrid, and Exchange Online: queries with sample output, how to read the SMTP log correctly, and the issues that regularly lead to incorrect conclusions.
Who Is Actually Delivering to Your Tenant? Aggregating Sending IP Addresses
A single report shows which systems actually deliver mail to your tenant: forgotten connectors, applications sending directly, and service providers nobody documented, including the typical analysis errors involving pagination logic and interpretation.
Common Causes of Mail Loops and How to Fix Them
How to systematically identify and fix SMTP mail loops in Exchange Online, hybrid environments, and upstream mail gateways using NDRs, headers, Message Trace, recipient objects, and connectors.
EXO Migration Without a Remote Move
How to provision on-premises Exchange mailboxes in a controlled manner as new, empty Exchange Online mailboxes: PST backup, CSV approval, RemoteMailbox, synchronization, validation, and rollback.
Ghost Sender in Exchange Online: An MX Record Is Not a Firewall
Direct delivery to Exchange Online bypasses an upstream gateway if the tenant does not explicitly block it. The risk is real; the cause is an incomplete mail flow configuration.
Access Exchange Online with PowerShell: Replace EWS with Microsoft Graph
EWS ends in Exchange Online on October 1, 2026. Learn how to register an app, authenticate a PowerShell script using a certificate, restrict access to individual mailboxes, and process messages and attachments through Microsoft Graph.
