Unlike Gmail, it’s correct you can actually encrypt your messages in Outlook using:
• digital IDs (certificates) for sender and recipients (S/Mime)
• Office 365 Message Encryption (OME), or
• email encryption add-ins

How do these options compare to using PrismCipher?

S/Mime. This option works with any email account that you have added to Outlook. It requires your recipients to also use Outlook (or an S/Mime compatible email application). All recipients must also install and share encryption certificates. This option won’t work if you need to send encrypted email to free webmail users like Gmail or Yahoo. This is probably the most technical option.

OME. This option does not require installing certificates. It lets you send encrypted messages to any email recipient, but it’s only available if you use an Office 365 email account (Outlook). Also, you need the Outlook application installed as part of the Office 365 subscription (this encryption option is not available in Outlook 2013, Outlook 2016, or Microsoft Office one time license purchases). This is likely the most expensive option.

Add-ins. The right encryption add-in, such as PrismCipher, lets you send encrypted email to any recipient, including free webmail users, using any email account from a supported service. This option is the easiest to employ—it’s the least technical—and is also free. “Software” installation isn’t even necessary; all you have to do is install a simple browser extension.