Downloading the microsoft exchange server 2016 download 64 bit iso fixed new is free. Running it in production requires a license.

You can install and use the ISO in trial mode for 180 days without a key.

First, do not look for a 32-bit version. Exchange Server 2016 is exclusively 64-bit. It will not install on 32-bit hardware or OS. You need:

From the ISO root:

Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms
Setup.exe /PrepareAD /IAcceptExchangeServerLicenseTerms
Setup.exe /PrepareAllDomains /IAcceptExchangeServerLicenseTerms

Then, launch the GUI setup wizard:

The "Fixed" Advantage: In early CU builds, schema preparation would fail if any domain controller was offline. The new ISO handles replication waits gracefully.

If you previously installed an older Exchange 2016 RTM or CU3 ISO (e.g., from a forgotten backup), you do not need to uninstall. The fixed new ISO can perform an in-place upgrade:

Warning: Direct upgrades from CU10 or older may fail. You may need to install intermediate CUs (CU15 → CU23). Consult the Microsoft Exchange Deployment Assistant.