The Publish to Global Address List (GAL) button must be disabled in Outlook.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-223355	SRG-APP-000516	O365-OU-000010	SV-223355r961863_rule	2025-03-05	3

Description
This policy setting controls whether Outlook users can publish e-mail certificates to the Global Address List (GAL). If you enable this policy setting, the "Publish to GAL" button does not display in the "E-mail Security" section of the Trust Center. If you disable or do not configure this policy setting, Outlook users can publish their e-mail certificates to the GAL through the "E-mail Security" section of the Trust Center.

Description

This policy setting controls whether Outlook users can publish e-mail certificates to the Global Address List (GAL). If you enable this policy setting, the "Publish to GAL" button does not display in the "E-mail Security" section of the Trust Center. If you disable or do not configure this policy setting, Outlook users can publish their e-mail certificates to the GAL through the "E-mail Security" section of the Trust Center.

ℹ️ Check
Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Cryptography >> Do not display 'Publish to GAL' button is set to "Enabled". Use the Windows Registry to navigate to the following key: HKCU\software\policies\microsoft\office\16.0\outlook\security If the value for publishtogaldisabled is REG_DWORD = 1, this is not a finding.

✔️ Fix
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Cryptography >> Do not display 'Publish to GAL' button to "Enabled".