When installing or reinstalling the MSA, you get the following error:
Messaging Security Agent failed to be installed on the Exchange server: sunmail
The operation will continue until it is completed even if the window is closed.
Internal Error 2753: instISDeferredCustomActionSt
To resolve the issue:
- Open the Registry Editor (regedit.exe). Always back up the whole registry before making any modifications. Incorrect changes to the registry can cause serious system problems.
- Delete the following registry key:
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\UpgradeCodes
\F79BAC82EE02C8A4CB43EE3AB234B806] - Reinstall the MSA.