[Exim] Majordomo and Exim

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I recently upgraded exim from 3.14 to 4.12 and afterward started getting a lot of messages from Majordomo (as the Majordomo-owner) of the nature that Majordomo wasn't going to reply to Mailer-Daemon to avoid a mail loop. I've tracked down in the exim log the line where the message is being sent to Majordomo and then forwarded on to me. Unfortunately I'm not clear what everything on the line means. The line is as follows:

2003-03-22 14:46:17 18wqoj-0004Sd-00 <= <> R=18wqjd-0004NG-00 U=mail P=local S=5372

What I do understand about this line is that the sender is blank (from the Mailer-Daemon), the message id listed after the R= is the message that was being sent out by Majordomo to the mailing list, the U=mail probably indicates the user id as mail, P=local seems to mean the message is coming from the local machine (local postoffice?) but what the R= means or the S=5372 is unclear. Can anyone shed some light on this?
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