Lists which are configured to either add a trailer, remove certain mime components, or munge the Subject header are susceptible to Y!'s DMARC configuration.
The munging is visible in this email message right on the From: line. However it will not impact attempts to send me direct replies since Y! also sets an (unmunged) Reply-To header. Had I not done this many/most of your mail servers would have rejected this email from being delivered to you. I consider this solution an acceptable tradeoff that does not force you to make any compensating changes to your current list config.
