All my servers use mailx with ssmtp to send email messages via my Postfix mail server for events and scripts.

I've noticed quite a lot of bounce back messages going from the mail server "MAILER DAEMON" back to each root@host.mydomain.com which of course doesn't get through since there is nothing to receive it on the hosts.

This leaves stuff stuck in the queue until it is dropped by Postfix, the MTA on the mail server. Snort then alerts on these failed connection attempts as port scans which is also annoying.

Is there a way to tell Postfix to not do bounce backs to *.mydomain.com so that the messages are immediately dropped if failed with a notifications to postmaster (which is aliased to me).

I'd also like to know why they are being bounced, is there a way to look inside the emails in the queue?

As to why the mail is being bounced, look in the mail log ( something like /var/log/maillog ). You can use postcat to read the files in the queue.

Instead of telling postfix to drop messages, it might be better to put a valid return address on outgoing messages from the ssmtp machine. That way, you'd be able to read any future bounce messages and know when and why they occurred.