If of use this is my local_decoder.xml file for OSSEC Code:
<!--
Zimbra OSSEC
-->
<decoder name="zimbra">
<prematch>^\d\d\d\d-\d\d-\d\d \d\d:\d\d:\d\d,\d+ WARN|INFO</prematch>
</decoder>
<decoder name="zimbra-preauth-failed">
<parent>zimbra</parent>
<prematch offset="after_parent">[\S+] [\S+] security - cmd=PreAuth; account=\S+; admin=\S+; error=authentication failed for \S+, preauth mismatch;$</prematch>
<regex>[name=(\S+);ip=(\d+.\d+.\d+.\d+);]</regex>
<order>user, srcip</order>
</decoder>
<decoder name="zimbra-preauth-passed">
<parent>zimbra</parent>
<prematch offset="after_parent">[\S+] [\S+] security - cmd=PreAuth; account=\S+; admin=\S+;$</prematch>
<regex>[name=(\S+);ip=(\d+.\d+.\d+.\d+);]</regex>
<order>user, srcip</order>
</decoder>
<decoder name="zimbra-unknown-account">
<parent>zimbra</parent>
<prematch offset="after_parent">account not found$</prematch>
<regex>[oip=(\d+.\d+.\d+.\d+);\S+] SoapEngine - handler exception: authentication failed for (\S+),</regex>
<order>srcip, user</order>
</decoder>
<decoder name="zimbra-invalid-password">
<parent>zimbra</parent>
<prematch offset="after_parent">invalid password$</prematch>
<regex>[name=(\S+);oip=(\d+.\d+.\d+.\d+);\S+]</regex>
<order>user, srcip</order>
</decoder>