Emails that you share using shared labels are not stored on Hiver’s servers. Please note that the emails might stay on Hiver’s servers for upto 1 hour while they are being synced between Gmail accounts. But this is temporary storage, and is cleaned up automatically.
Do also note that we store the message ids of your emails, and might store the subject of some of your emails in our database. This is required for the syncing of emails across accounts to work.