Across Europe, only 82.2% of legitimate marketing e-mails reached subscribers’ inboxes, down from 85.4% reaching the inbox in the second half of 2009. Earlier this week, Return Path released the results of their bi-annual deliverability benchmark report, and the news for senders is not encouraging.

Return Path hasn’t yet released updated figures for North America, but in the last half of 2009, the numbers were similarly grim: 20% of e-mail in the United States and Canada is still not making it to the inbox while 3% of e-mail goes to the “junk” or “bulk” folder and another 16% goes missing altogether. Only incorrigible optimists are expecting anything other than worse news when the updated numbers are released.

What’s driving this steady erosion in overall deliverability performance? It’s tempting to place the blame squarely on the shoulders of the ISPs that do the actual filtering, but that’s not the whole story. By some accounts, up to 94% of the total, unfiltered e-mail volume worldwide is comprised of spam, most of which is generated by armies of compromised computers under the control of criminal spam gangs. ISPs are forced to use ever more aggressive tactics to protect their users from spam, and make sure that just the wanted mail is delivered.

This is an important point that’s often lost on senders who find themselves on the wrong side of the ISP’s filters: delivering mail that customers want is as important for as blocking the spam. Within the last few months, major inbox providers like Hotmail and Gmail released new versions of their offerings that measure how recipients interact with your mail – whether they open it, how often they click through, even how much time they appear to spend reading a particular message. (Yahoo! and AOL are preparing similar changes in the coming months.) The more engaging and relevant your mail appears to be, the more often it will land in the inbox.

It takes work to find out what engages your recipients – typically an iterative process that requires testing and careful measurement – but it’s a lot easier than convincing an ISP that your mail is wanted in the absence of supporting engagement metrics. One easy way to find out what recipients want is to ask them. Use the Real Magnet survey tool to find out if they want to know about sales or specials, industry-specific news, free webinars, or some mix of all of these – and how frequently they want them. Ask them about other content-areas of interest. If you’re a retailer of Irish-themed gifts an apparel, for example, readers might want to see short vignettes or links to stories about Ireland next to your offer. Then deliver what they ask for (and nothing else!).

E-mail frequency plays an important role in engagement, too. Use recipient-level tracking in Real Magnet to identify those recipients who haven’t opened or clicked in a while – they may be suffering from “inbox fatigue”. Give them a rest from future sends for a while, and come up with a sharp offer – like a coupon code or a discount for your webinar – to re-engage them with. Avoid recurrences of fatigue with a subscription preferences page where they can specify their preferred frequency. If they still show no signs of engagement, you may want to suppress them from future sends.

Try the built-in A/B testing functionality to measure response to different subject lines and calls to action. Sometimes changing a single word in your subject line can make all the difference in open rates. Test different versions on small groups you create in Magnet Mail just for testing purposes. Identify the changes that result in the biggest gains in opens, and roll them out to the rest of your recipients.

It’s tempting to shake one’s fist at the sky and bemoan mistreatment at the hands of uncaring e-mail gods, but senders really are in control of their own destiny. Real Magnet has the tools senders need to make optimization for delivery and engagement easier than they think.