Gregory's Server
* Upon sending an email out of the third party email client, the user can't possibly know whether the email is actually going to be send end-to-end encrypted (the client can't show this as a bridge works on a different level). Therefore sending confidential emails via a bridge is essentially impossible...
* IMAP and SMTP are not the most efficient protocols especially when it comes to push notifications or to attachments of emails (which are encoded into the body).