I have a zimbra mail server that sends mails from application to their subscribers. As the e-mails are not verified during signup users tend to give wrong address. This is having an impact on mail server reputation sending out mails. Is there a way to:

1. Check if user exists before delivering messages. If the other MX sends a non-existence reply (hard bounces), can we create a database and not send mails from mail server (not application). I mean drop transport.
2. If there is an error that domain or MX does not exist, update database for domains and not send mails to this domain for n days?

Any help in this regard is appreciated.