For now, the encryption plugin is only available on the older version, Nylas Pro. No reason for that other than time to port and QA the plugin to the new free version, which has a completely written mail sync engine that runs locally rather than in the cloud. We're working on porting all Nylas Pro features to the new version as fast as we can!
If you want to keep up to date about the latest features, you can sign up for our newsletter at the bottom of this page: https://nylas.com/nylas-mail/
If you want to keep up to date about the latest features, you can sign up for our newsletter at the bottom of this page: https://nylas.com/nylas-mail/