Nifty feature.
It's still recommended to use a desktop client where able so that your private key(s) are stored locally, and not server-side. But for general use and for convenience, you can now send/receive encrypted emails from webmail.
Emails are sent/received fully encrypted and decrypted at the origin.
Rambler OP wrote
And yes, you can access your @your-domain.com webmail over Tor, as well. Still working out some I2P integration kinks, but Tor is good to go right now.