Odhiambo Washington writes:
An organization is 'sponsoring' a list and wanted to have their logo included on all messages on the list. I understand that this means the list has to somehow modify the message as it leaves going to subscribers.
I would think so, yes.
I was thinking you could abuse the X-Face or Face headers, but apparently they're only supported by a few MUAs popular on Linux.
As regards "convert_html_to_plaintext" I can have that disabled if it will allow me to include the sponsor's logo somewhere in the body of the message, but footer is best option.
Including in the footer is probably not an option for a plain text message. It probably would only take a few lines of Python code to attach the file as a MIME part in a custom Handler, but then the presentation would be up to the users' MUAs, and it seems likely to be ugly.
For HTML messages, I think there was some way for Mailman to insert the footer material in the HTML rather than attach it, but that was probably a 3rd party patch. It's also unreliable because you have no idea what formatting a given MUA may put in its HTML, but you probably can tune it to give good results for the most popular MUAs used by the list's posters.
Again for HTML messages, it might be possible to do something tricky with an <IFRAME> element to hold the original message, and put the footer at the bottom of the main BODY. (The original message would live in a separate MIME part and the src= ref would use the cid: URI scheme.) I think this would work pretty well in most modern browsers, but I don't know how smart the MUAs would be. (Completely untested, I don't even have a proof of concept.)