I would like to ask some recommendations on this scenario.

We are using our zimbra mail as a forwarder to different emails.

For example, our domain is makoy.com, and then we use group1@makoy.com as a forwarder to user1@yahoo.com,user2@yahoo.com,user3@yahoo.com... user10@yahoo.com. We have a total of 8 groups, and many clients/users are sending messages to these groups frequently and some are also being CCd to email loops.

Most of the time we receive the emails late because messages are being deferred because of the error " Receiving "421 4.7.0 [TS02] Messages from x.x.x.x temporarily deferred -" when sending email to Yahoo! "

I think that Yahoo is thinking/detecting that the zimbra mail server is sending SPAM messages that is why it is being deferred. Is there a way to fix this problem?

I hope you get what I am trying to say. Thanks and Cheers!