A recent conversation about the vagaries of HTML e-mail on the Progressive Exchange mailing list prompted some good conversation about a perennially vexing topic: how do you keep your hard-won html design rendering properly in your recipients' mailboxes?

Short answer: you probably don't.

For coders who like to get into it, I've been in the habit of recommending the exhaustive sleuthing done by sorta-competitor Campaign Monitor (for instance), which blogs the bejeezus out of the issue and has great resources like 30 free design-compliant templates that might shortcut the process.

The thumbnail version for the rest of us is that there's no orthodoxy. Like 4th century heretics, every e-mail provider has its own slightly different standard which on pain of hellfire and junk filtering is incompatible with every other provider's standard.

What's a small organization without the luxury of coding line-by-line styles to do?

One solution, quite possibly the best cost/benefit option, is to move either to text-based messages or to HTML messages that are little more than text. (The latter preserves tracking options that text-only messages lose.)

Your readers might thank you for it. MoveOn, nobody's idea of an online communications dummy, has had predominantly succinct, graphics-lite, white space-heavy messages for some time now.

If you're sticking with any amount of HTML at all, you need to be aware that you'll never have complete control over what the user ends up seeing ... and messages read in an online mail client like Yahoo or Hotmail introduce the complication that styling elements that make Yahoo look like Yahoo "wrap" your HTML message and might conflict with it.

With that in mind, I've searched the DIA universe for the most common e-mail domains on mailing lists. (DIA users can see for themselves the domain distribution of their blasts in their e-mail reports.)

The Big Four

If you do nothing else whatsoever, you simply have to sign up for free accounts and test these out for a list of any appreciable size. The percentage figure is the percent of all DIA supporter records with e-mail addresses who use this domain.

Yahoo: 16.8% When including its various overseas forms (@yahoo.fr, for example), Yahoo's share rises to 17.4%.

Hotmail/MSN: 14.3%

AOL/AIM: 11.5% I'd love to see a demographics breakdown for AOL. Their reputation as your parents' mail provider, if accurate, would be useful for fundraisers who know that the parents have all the coin.

Gmail: 3.8% Big drop from the "big three" to Gmail, whose lead for fourth place isn't that initially tremendous. But bear in mind that the Google cachet and the tagging messages feature mean that it's disproportionately common for messages to other domains to be read in the Gmail interface. Google is also characteristically bleeding edge, and a likely place to preview the adaptations you'll have to make for Yahoo 12 or 18 months later.

Though the list above probable won't surprise anyone, it's notable how commanding their position is: right around half of all e-mails in our universe (and an overwhelming preponderance of webmails), with thousands of other domains comprising the other half.

Smaller online services, ISP-based addresses, non-US domains and the host of miscellaneous .edu, .org, .gov, and workplace or boutique .com addresses are all relative drops in the bucket, only a handful of the larger ISPs (Comcast, Earthlink, SBCGlobal, Verizon, Cox and Juno -- in descending order) cracking the 1% line.

Update: Just to complete the thought here, for smaller groups with limited time, focus on knowing what your messages look like in these environments and making sure that there's nothing catastrophically wrong. Fighting to insure one's precise font definitions obtain everywhere is probably wasted effort unless the mail client's behavior really undermines your message.

Remember also -- another reason that Gmail will be useful -- to be sure to check out the image-less version of your message, which a steadily increasing proportion of subscribers will be seeing.