Exchange Online

Email Security Foundations #06 – DKIM: key rotation, third-party senders and troubleshooting

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This post is part of the Email Security Foundations series on MSDigest.net. Rotating DKIM keys Key rotation is good practice. If a private key is ever compromised, rotating limits how long an attacker can use it. Exchange Online makes this easy. How to connect to Exchange Online using PowerShell to rotate the DKIM Keys. After rotation Exchange Online switches to the other selector automatically. The old selector stays valid for a while so messages already …

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Email Security Foundations #05 – DKIM deep dive: signing, selectors and how verification works

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This post is part of the Email Security Foundations series on MSDigest.net. What DKIM actually does DKIM stands for DomainKeys Identified Mail. Where SPF checks where a message came from, DKIM proves that the message hasn’t been changed while it was in transit. When you send an email, your mail server adds a cryptographic signature to the message. When the receiving server gets it, it looks up your public key in DNS and uses that …

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Is Your On-Premise Exchange Server Ready for March 22nd 2026?

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If you run an on-premises Exchange Server or any Windows-based SMTP relay that sends mail to or receives mail from Exchange Online, then you might have a hard deadline coming up: March 22, 2026. Miss it, and you can risk breaking your mail flow, if the Root Certificates used by Exchange is not updated. What Is Changing Microsoft Exchange Online is switching its TLS certificates to the DigiCert Global Root G2 certificate authority. This is …

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Email Security Foundations #02: SPF, DKIM, DMARC, DANE, MTA-STS and BIMI explained

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This post is part of the Email Security Foundations series on MSDigest.net. The goal of the series is simple. Explain SPF, DKIM, DMARC, DANE, MTA‑STS, and BIMI in a way that actually helps Microsoft 365 admins run safer email. Before we go deep, here is the map In post #01 we looked at why email authentication still matters and why spoofing is still so effective. Before diving into each technology on its own, it helps …

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Email Security Foundations #01: Why email is still the most dangerous attack surface

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This post kicks off the Email Security Foundations series here on MSDigest.net. It’s a practical, no‑nonsense walkthrough of SPF, DKIM, DMARC, DANE, MTA‑STS, and BIMI written specifically for Microsoft 365 admins who want email to stop being the weakest link. Email spoofing remains one of the most effective attacks on the internet, largely because most organizations still allow it. The attack that really should not still work in 2026 A classic example is a Business …

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