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<blockquote>After installing security updates on Exchange servers do I need to extend schema on both Exchange servers?</blockquote><br>if there are any schema updates, it is done at the start of the update installation<br>the only time it would need to be done manually is if your account doesn't have rights in AD to extend the schema and someone else needs to do it (which would be done first before the exchange update)<br>otherwise, use an account part of the domain admins/schema admins/enterprise admins and run the installer and it will extend the schema automatically<br><br><blockquote>If I understood correctly for Exchange 2013 CU 23...</blockquote><br>yes<br><br><blockquote>And for my Exchange 2016 CU 20 I need to download Exchange CU 21(6.6 GB)...</blockquote><br>yes...2016 CU updates are the full installation product<br>it will detect the previous version and do the upgrade
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A last CU always contains all precedent CU.<br><br>Installing a CU that needs a schema update, will automatically update the schema if you have the correct permission (Member of Schema admin group).<br>If you don't have the correct permissions, the upgrade is not done until you use an adequate user, or the schema is updated by another authorized admin.
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I have Exchange 2013 CU 23.How can I install CU 24 if it doesnt exist? Im talking about regular July patch fir Exchange that requires schema update <a href="https://techcommunity.microsoft.com/t5/exchange-team-blog/released-july-2021-exchange-server-security-updates/ba-p/2523421?WT.mc_id=M365-MVP-5000284" rel="ugc">https://techcommunity.microsoft.com/t5/exchange-team-blog/released-july-2021-exchange-server-security-updates/ba-p/2523421?WT.mc_id=M365-MVP-5000284</a>
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Andy

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Hello,<br>I need to instal Exchange July security updates<br><a href="https://techcommunity.microsoft.com/t5/exchange-team-blog/released-july-2021-exchange-server-security-updates/ba-p/2523421?WT.mc_id=M365-MVP-5000284" rel="ugc">https://techcommunity.microsoft.com/t5/exchange-team-blog/released-july-2021-exchange-server-security-updates/ba-p/2523421?WT.mc_id=M365-MVP-5000284</a><br>My current environment:<br>Exchange 2013 CU 23&nbsp;<br>Exchange 2016 CU 20<br>Hybrid<br>I’m in the middle of migration.<br>After installing security updates on Exchange servers do I need to extend schema on both Exchange servers?<br>If so,in what order?<br>If I understood correctly for Exchange 2013 CU 23 I need &nbsp;navigate(cmdàrun as admin) to C:\Program Files\Microsoft\Exchange Server\V15\Bin and run “Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms”<br>And for my Exchange 2016 CU 20 I need to download Exchange CU 21(6.6 GB) ,mount it and find setup for CU21 and run run “Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms”<br>Any advice<br>Thank you
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Hello,
I need to instal Exchange July security updates
https://techcommunity.microsoft.com/t5/exchange-team-blog/released-july-2021-exchange-server-security-updates/ba-p/2523421?WT.mc_id=M365-MVP-5000284
My current environment:
Exchange 2013 CU 23 
Exchange 2016 CU 20
Hybrid
I’m in the middle of migration.
After installing security updates on Exchange servers do I need to extend schema on both Exchange servers?
If so,in what order?
If I understood correctly for Exchange 2013 CU 23 I need  navigate(cmdàrun as admin) to C:\Program Files\Microsoft\Exchange Server\V15\Bin and run “Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms”
And for my Exchange 2016 CU 20 I need to download Exchange CU 21(6.6 GB) ,mount it and find setup for CU21 and run run “Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms”
Any advice
Thank you

Exchange security update

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.