Minimum encryption settings
The `minenckey` value defines the minimum encryption-key length against which Outlook evaluates encrypted e-mail messages for the current user.
since 0.9.8.11
Purpose
Show registry keys (1)
HKCU\software\policies\microsoft\office\16.0\outlook\security\minenckey
The minenckey value defines the minimum encryption-key length against which Outlook evaluates encrypted e-mail messages for the current user. It is a REG_DWORD; its data represents the key length in bits.
When the encryption key used for a message is shorter than this threshold, Outlook displays a warning before sending the message. This setting does not select an encryption algorithm or force Outlook to replace the key with a longer one.
Notes
Security
The warning identifies messages whose encryption key falls below the specified minimum. This can alert users before they send data using a weaker key.
The value is not an enforcement boundary by itself. Users can disregard the warning and send the message with the originally selected key. Preventing that override requires the separate Outlook policy that removes the Continue option from encryption warning dialog boxes. Consequently, minenckey alone does not guarantee a particular cryptographic strength or enforce a minimum key length for every sent message.
Possible side effects
Encryption configurations that use shorter keys generate additional warning dialogs. A threshold higher than the available or selected key size can therefore interrupt the sending workflow and require a user decision, although this value alone does not block transmission.
Notes
This setting applies to encryption-key length for Outlook e-mail messages. It does not govern TLS protection for server connections, Outlook RPC encryption, or encryption of files at rest.
Microsoft continues to list the policy for Microsoft Outlook 2016 and other Office products that use the 16.0 policy branch. The detailed public description of its warning behavior is found in documentation for earlier Outlook releases. When treated as a dependent Outlook security policy, it also relies on Outlook Security Mode being set to use Outlook Security Group Policy.
Microsoft documentation
Microsoft Learn: List of settings for the Microsoft 365 Apps for Enterprise security baseline
Microsoft: Security and privacy considerations for Outlook