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The question's title says it all.

Scenario: The Postfix server is used only for mail-relay; in the office back-end, we use hMailServer. Some hMailServer users have their emails auto-forwarded to their BlackBerry account. Sometimes, they changed their BlackBerry operator without informing IT Dept. As a result, the auto-forward (handled by Postfix) failed, and a notification is sent (by Postfix) back to the user's account, which gets re-forwarded to the (no longer active) BlackBerry account, another failure, and ... well, you get the idea: A mailing loop.

I need to prevent this from happening. For complex reasons, we can't change our current setup of a separate internal mail server and the cloud-based Postfix mail-relay. So, I must either reconfigure Postfix or use some other mail-relay system that can be configured as such.

Thanks in advance.

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Based on the title, I think the bounce_size_limit option might help. Try setting it to 0.

Based on the question body, I think you need something else.

Is this what's happening?

1. hMail ---> Postfix (OK)
2. Postfix ---> BlackBerry (Fails)
3. Postfix ---> hMail (OK)
4. hMail ---> Postfix (loop)

If so, you could append a header to the message as it's being forwarded at step 2, then see if that header is present at step 4.

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