This is really two questions in one. First, are nettiquette guidelines still accurate in their restrictions on ASCII vs. HTML, posting style, and line length? (Here's a recent metafilter discussion of the topic.) Second, If they are not, should these guidelines be respected? If they are (or if they should still be respected), how can modern mail programs be configured to work properly with them?
Most mailing list etiquette statements appear to have been written by sysadmins who loved their command lines, and refuse to change anything. Many still reference rfc1855, written in 1995. Just reading that paginated TXT should give you an idea of the climate at the time. Here's a short, fairly random list of mailing list etiquette statements with some extracted formatting guidelines:
Mozilla - HTML discouraged, interleaved posting.
FreeBSD - No HTML, don't top post, line length at 75 characters.
Fedora - No HTML, bottom-post.
You get the idea. You've all seen etiquette statements before.
So, assuming that the rules should be obeyed (Usually a good idea), what can be done to allow me to still use a modern mail program, and exchange mail with friends who use the same programs? We like to format our mail. Bold headings, code snippets (sometimes syntax highlighted, if the copy-paste pulls RTF text as from XCOde and Eclipse), free line breaks determined by your browser width, and the (very) occasional image make the message easier to read. Threaded conversations are a wonderful thing. Broadband connections are, I'm sure, the rule for most of the users of SU and of developer mailing lists, disk space is cheap, and so the overhead of HTML is laughable.
However, I don't want to post a question to a mailing list and have the guru who can answer my question automatically delete it, or come off as uncaring. Until I hear otherwise, I'll continue to respect the rules as best I can.
For a common example of the problem, Gmail, by default, sends HTML formatted messages with bottom-posted quotes (which are folded in, just read the last message immediately above), and uses the frame width to wrap lines, rather than a character count. ASCII can be selected, and quotes can be moved and reversed, but line wraps of quotes don't work, line breaks are tedious to add (and more tedious to read, if they're super small in comparison to the width of the frame).
Is there a forwarding, free mail program which can help with this exercise? Should an "RFC1855 mode" lab be written? Or do I have to go to the command line for my mailing lists, and gmail for my other mail?