Note: This feature is for ZCS Network Edition only and is available only in the Advanced Zimbra Web Client.
If the S/MIME feature is enabled for your account, a Security page is available in your ZWC Preferences.
The default setting for the Security preference is to automatically remember the last security option you selected when you composed an email.
You can change the default preference to always send your messages as signed; as signed and encrypted, or to not sign or encrypt your messages. You can change the option from the Security tab in the compose page, but the change is only for that message.
Click Preferences.
In the Overview pane, click Security.
Change the settings.
Auto (remember last settings) is the default. The last security option you select is remembered
Select Do not sign or encrypt if you do not use the S/MIME feature at all or rarely
Select Sign only if you always send your email with a digital signature
Select Sign and encrypt of you always send your email with a encrypted with a digital signature
Click Save.