Procmail (or the custom binary) was removed or replaced by a stub that returns a non-zero exit code. Many distributions removed Procmail by default after 2020.
The key to resolution is identifying the specific transport (pipe, LMTP, smtp) that is failing, checking the system logs for underlying errors, and verifying that the external binary or socket is functional when invoked manually by the postfix user. Procmail (or the custom binary) was removed or
This article provides a deep dive into the root causes of this error, specifically focusing on scenarios that arise . We will explore why this happens, how to diagnose the exact issue, and step-by-step solutions to restore normal mail flow. Understanding the Error: What Does It Mean? In Postfix terminology, a transport is the method by which a message is delivered to its final destination. This could be a local mailbox (e.g., using local transport), an LMTP socket, a Dovecot deliver agent, or a relay host (e.g., smtp transport). This article provides a deep dive into the