Exchange Server: "The message has been deferred by the categorization agent"

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At the turn of the year, there is a problem with mail delivery on Exchange servers. Mails get stuck in the queue with the following message: "The message was put on hold by the categorization agent" Mails are neither sent nor received. This problem has been occurring on all Exchange 2016 / 2019 servers since 01.01.2022 and is caused by the transport agent "Malware Agent" ... Read more

Happy New Year!

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I wish all visitors, readers, supporters and friends a happy and healthy new year, may all your good intentions and wishes come true in the new year. As every year, I would like to take this opportunity to look back on the past year. Visitor numbers have risen again slightly in 2021. Just under 2.5 million visitors are ... Read more

Merry Christmas!

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I wish all friends, readers and supporters a Merry Christmas, take care of yourselves and stay healthy. I wish all admins who are looking after the well-being of the systems during or between the holidays every success. Take a few days off as soon as possible and treat yourselves to something nice. As in every ... Read more

Exchange 2019: Setting up a hybrid environment (part 5)

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The Exchange 2019 hybrid environment has already been set up in Part 4. I actually wanted to go into the migration batches in more detail in this article, but decided against it. The migration batches and their options are usually only relevant in larger environments. In smaller environments, the migration batches can be conveniently set up via the Exchange Online Admin Center ... Read more

Exchange: Delete old OWA/ECP data

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Exchange Server leaves old data or versions of the OWA and ECP directories on the file system after almost every update. In particular, the directory "C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa\prem" takes up a lot of space on the file system after a long runtime and correspondingly many updates. Here is an example of an Exchange Server that has been running for a while: Old file versions ... Read more

Exchange 2019: Setting up a hybrid environment (part 4)

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The fourth part of this article series deals with the necessary adjustments to the DNS and the first tests. In part 3, the Exchange Hybrid configuration was completed to such an extent that only a small amount of configuration is now required. Essentially, once the SPF entry has been adjusted, the tests can begin. Adjust DNS settings (SPF) So that ... Read more

Install Exchange security updates urgently

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There are currently still many Exchange servers that have not been provided with the urgently needed security updates. This is not only about the ProxyLogon and ProxyShell vulnerabilities, which were already closed in April by corresponding updates, but now also about the vulnerability CVE-2021-42321, which has been closed with the latest Exchange updates. About the exploitation of ... Read more

Exchange 2019: Setting up a hybrid environment (part 3)

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In the previous article, the Microsoft 365 Tenant and Azure Active Directory Connect were set up. This article now deals with the installation and configuration of the Hybrid Configuration Wizard (HCW). The HCW creates the Exchange Hybrid environment and enables you to migrate mailboxes from the Exchange on-prem installation to Microsoft 365. The HCW takes over all ... Read more

Security updates for Exchange Server (November 2021)

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Microsoft has released new security updates for all supported Exchange Servers (2013, 2016, 2019). In particular, Microsoft mentions the vulnerability CVE-2021-42321 (Remote Code Execution) in Exchange 2016 and 2019, which is already being exploited in a limited number of targeted attacks. The number of attacks is likely to increase as the update may now make the vulnerability easier to detect. ... Read more