Hello, after adding a second DNS ( to my resolv.conf:

nameserver localhost # bind9 is installed
nameserver # open dns server

I have the following problem in the zimbra.log:

May 20 07:08:22 vmx-ext-fi-1 postfix/lmtp[6997]: 5DBF32F2646: to=<username@mydomain>, relay=none, delay=34212, delays=34022/0.11/189/0, dsn=4.4.1, status=deferred (connect to vmx-ext-fi-1.mydomain[]:7025: Connection timed out) is not my public IP address but it is open DNS!!

As a result mail is not delivered to mailboxes and all messages remain in the deferred queue.

What is to blame? my configuration or Open DNS?
I added the second DNS Server because with 'localhost' I cannot 'dig zen.spamhaus.org'. (I'd like to solve this issue too but I don't know how)
Is it correct to add a second DNS server in a ZCS installation?
What is the best practice?