Out-of-office replies work best where they can run without you: on your provider's servers. Set up that way they answer every message the moment it arrives, overnight, and with your phone switched off or BlueMail closed.
Set one up with your email provider, in their web interface: Gmail's Vacation responder, Outlook's Automatic replies, and the equivalent in Yahoo and most other providers. Because it runs on the provider's server, it keeps replying while your phone is off and applies to every device you read that account on, which a mail app cannot do.
BlueMail will show the replies it sends in your Sent folder like any other outgoing mail.
