Sendmail still is being used on the majority of mail hubs. Sendmail has very primitive loop detection, bouncing messages based on excessive “hopcount”. The “hopcount” is determined by counting ‘Received:’ headers. ezmlm by default propagates ‘Received:’ headers to facilitate message tracking. Thus, messages, especially from a sublist, can have a number of ‘Received:’ headers that exceeds the “hopcount” set on poorly configured sendmail hosts. Subscription confirmation requests, warning, and probe messages have fewer ‘Received:’ headers. Thus, a user may be able to receive these, but not (some of the) list messages. Of course, the best is to correct the configuration on the bouncing host, but this is often under the control of neither list owner nor user.
To compensate for this problem, ezmlm-send(1) of ezmlm-idx->=0.313 by default removes all ‘Received:’ headers except the top one. They are still written to the archive, an can be retrieved from there using the -getv command. To cause ezmlm-send(1) to pass on all the ‘Received:’ headers, use the ezmlm-send(1) -r switch.