Isn't that just CYA? Thank the lawyers and "corporate compliance
offices" and professional whiners.
The obvious answer is that if your corporate email policy makes you look like an idiot, post to mailing lists from a personal email address that doesn't make you look like an idiot.
This also spares the list from "out-of-office" messages from Exchange servers too stupid to refrain from sending such messages to mailing lists.
Regards,
Tim.