I was thinking of my MTA settings since many of the mails in the deferred queue originates from a box on another network. Right know my postconfig mynetworks returns
"127.0.0.0/8 10.10.10.64/26"
10.10.10.64 is the mail servers broadcast. 10.10.10.119 is its actual IP.
but I guess I would also need to add a half C-class like this 11.11.11.128-255.
Sadly, I'm not sure howto and I can't find any resources that explains it.
Outgoing Mail Problems - Zimbra :: Wiki
After some digging I think I added the external subnet correctly.
Running zmprov gs `zmhostname` | grep zimbraMtaMyNetworks now returns
zimbraMtaMyNetworks: 127.0.0.0/8 10.10.10.64/26 11.11.11.128/25
Code:
Nov 6 16:37:20 mail zimbramon[14253]: 14253:info: zmmtaconfig: Skipping Global system configuration update.
Nov 6 16:37:20 mail zimbramon[14253]: 14253:info: zmmtaconfig: gacf ERROR: service.FAILURE (system failure: ZimbraLdapContext) (cause: javax.naming.CommunicationException mail.server.com:389)
Well, that didnt work. I removed the last subnet mask from the zimbraMtaMyNetworks.