Web UI and rejected emails

Hi, 

I have noticed that when sending an email using the web interface, if postfix rejects the email for any reason (ex: invalid email address, cbpolicyd, etc.) the web interface pops up a notice "Something went wrong. Please try again." and the email just stays in the Drafts folder. If a user sends an email to multiple recipients and only one of them is invalid, Carbonio will show the same error and not send the email to the valid email addresses.

Is there any way to have the web interface submit the email to postfix's queue and if postfix has any issue sending that email, providing a bounce back error message for the invalid recipients while delivering the email to valid recipients?