Code:
Mar 25 09:24:16 localhost postfix/lmtp[10228]: CA8139F06E2: to=, relay=none, delay=1, status=deferred (connect to mail.mydomain.info[71.xxx.xxxx.xxx]: Connection refused)
Notice this says LMTP which means it's postfix trying to deliver the mail to zimbra via lmtp on port 7025. postfix will always use DNS. So your DNS looks to be resolving mail.mydomain.info -> 71.xxx.xxxx.xxx.
Two ways to fix this. Set up split DNS so the internal DNS request from postfix gets the 192.x.x.x address.
or if you want a less secure hack open 7025 on your firewall to allow postfix to come in via the 71.x.x.x address and deliver. If you set the rule to only allow the localhost it'll be more secure and will keep your 7015 port hidden from the internet.