I've been working on a spare project using SNMP and Zimbra Collaboration. This project uses a modified version of the popular pflogsumm script to retrieve the Zimbra Collaboration email queues information and creates an output which we retrieve using the NET-SNMP-EXTEND, so we can monitor each sensor as an SNMP OID.
UPDATED
More information available in: https://github.com/jorgedlcruz/zimbra-net_snmp-extension
With this project you can monitor multiple things of a Zimbra Platform, fro example the Zimbra mail queues using the SNMP tool you prefer.
Zimbra Collaboration Performance
* Received Megabytes
* Delivered Megabytes
* Total Emails/received
* Total Emails/Delivered
* Total Recipients
* Total Senders
* Forwarded
* Deferred
* Bounced
* Rejected
* Held
* Discarded
* Domains Receiving Emails
* Domains Sending Emails
Also, and brand new, you can now monitor the service status, Version, License and License valid until:
These Scripts combine allow us to monitor from our Zimbra Collaboration:
* Zimbra Version
* Amavis Status
* Antispam Status
* Antivirus Status
* Convertd Status
* LDAP Status
* Logger Status
* Mailboxd Status
* Memcache Status
* MTA Status
* OpenDKIM Status
* Proxy Status
* Service Web App Status
* SNMP Status
* Spell Status
* Stats Status
* Zimbra Web App Status
* Zimbra Web Admin Web App Status
* Zimbra Configd Status
* Zimbra License Status
* Zimbra License valid until Status
Here are an example of how it might look like with PRTG and the Zimbra queues:

And this one just for Resources and Service and License status:

Coming next
This is just a v0.1 of this Dashboard, the next step will be to use the Zimbra SOAP API to obtain some extra information from the Zimbra Collaboration Environment, like:
* Number of Active Users
* Number of Inactive Users
* Number of Domains
* Number of Users with ActiveSync
* etc.
In next versions we will parse directly the logs and put the attempts of logins, and successful logins on a map.
As this is an open project, please feel free to share your ideas, feedback and if possible even help to make it better

Thank you guys!