Split domain: How to disable antispam of messages for non local delivery

[meesha]

Hi,

our schema is zimbra as primary, some other postfix mta like secondary. Zimbra catch all mails and which are not for local delivery, sends to secondary MTA.
Split Domain - Zimbra :: Wiki

Zimbra applied antispam checks for all messages - messages for local delivery and also for delivery to secondary MTA.

I cannot find how to disable antispam check of messages for non-local delivery - messages for secondary MTA.

I have tested one possibility with cos.
Every user has setted up manually COS with zimbraFeatureAntispamEnabled: TRUE

Domain has setted up different COS with zimbraFeatureAntispamEnabled: FALSE

zmamavisdctl restart
zmmtactl restart

And all messages are still checked by amavis...

Any idea how to make zimbra "transparent" (it means no antispam checks) for messages for delivery to secondary MTA?

Thank you.