That's right. All scheduled emails are encrypted and stored on Mail Boss servers. Regarding security, I believe that storing your scheduled messages on the server is actually more secure since it doesn't require any access to your Gmail account. The previous version of Mail Boss required you to grant permissions to read all messages in your drafts folder (because Gmail didn't provide granular enough permissions to further limit that access). With the new version, the only information you are required to trust with Mail Boss are the scheduled messages that you explicitly send to us. Even if the Mail Boss server was fully compromised, the attacker would not be able to gain access to your Gmail account since we don't have the access tokens that would be required to do that. That said, for your protection and ours, we recommend that you don't include any sensitive information in your scheduled messages.
Dustin