Many mailing list software returns header information (including, most importantly, From header) while making some modifications to the message (e.g., adding a footer or prepending some text to the Subject header).

A lot of owners reconfigured said software to rewrite the From header since Yahoo changed their DMARC policy to a hard fail and broke quite a lot of mailing lists in doing so, as the resulting backscatter caused the software to unsubscribe people from the mailing list when delivery failed if someone sent a message from their Yahoo account.