It's an Internet arms race that has spilled into all aspects of email marketing: As quickly as ISPs come up with new ways to fight spam, spammers find new ways to deliver it. Surveys indicate that the biggest challenge facing sophisticated email marketers is deliverability – getting your opt-in messages through the spam filters and into your recipients’ inboxes. But the problem isn't confined to huge brands like Lands' End or Walmart. In fact, the challenge for smaller businesses, especially those unfamiliar with email's thorny technical issues, can be formidable.

Deliverability is deceptively complex, and many marketers under-invest in the day-to-day processes that drive its successful execution. As a result, many do-it-yourselfers in particular suffer from exceedingly poor email deliverability—sometimes without even knowing it.

Here are eight things you can do to avoid being caught in the crossfire of the spam wars:

Never send commercial email to people who haven’t consented to receive it

It makes a poor brand impression, violates most ISPs' terms of service, and almost guarantees deliverability problems. If your recipients aren't anticipating your email, ISPs will go out of their way to make sure they don't get it.

Avoid spammy gimmicks

Your email shouldn’t resemble a bad Las Vegas lounge act. Spam filters seek patterns and irregularities often found in spam, so resist the temptation to spice up messages with all-caps, big fonts, weird punctuation, exclamation points, repeated phrases, or common advertising come-ons such as “free!” or “limited time offer!” It’s also a good idea to screen your messages with a spam filter such as SpamAssassin to flag any potential content problems before you send.

Practice good list hygiene

Spammers’ lists are littered with invalid and out-of-date information. One of the ways ISPs ferret them out is by watching for mailings with a high percentage of bad addresses. So, if an ISP “bounces” an address back to you as permanently undeliverable, scrub it from your list immediately. Strive for a hard bounce rate of no more than four to five percent. Anything above about seven percent is likely to impact your deliverability.

 Don’t ignore ISPs

Email marketers often don’t realize they need to set up an abuse@yourdomain.com mailbox in order for ISPs to be able to communicate information, such as bounce codes, back to a mailing’s origin. If you don’t have an appropriate mechanism for accepting an ISP’s messages, you’ll not only look like a spammer, but you’ll have no way of knowing what ISPs are trying to tell you in order to address problems and ensure your mailings continue to get through.

Keep volume low

If you are sending marketing email through your corporate server, you'll want to keep volume to a dull roar. Although the number varies wildly between ISPs, sending more than about 1,000 identical emails at a time is practically inviting an ISP to take a closer look and turn up the spam filters on what appears to be bulk email pouring from an interpersonal email server.

Protect your corporate IP address

Your Internet Protocol (IP) address is your unique “Internet address.” Always send your marketing email through a different IP address than the one you use for your corporate email. That way, if you run into deliverability problems, you don’t expose your corporate email to risk.  If the worst happens, and an ISP blocks your email marketing IP address, you can still carry on with your necessary day-to-day business-related email communications.

Implement authentication protocols 

Email authentication protocols such as Sender Policy Framework, Sender ID and DomainKeys help ISPs ensure email really is from the company claiming to have sent it. Microsoft’s surprise announcement in June that it would begin flagging email in its MSN and Hotmail services that fails a check of the Sender ID protocol sent companies scrambling to initiate compliance. Authentication will help address the problems of email “spoofing” and phishing, and ultimately will lead to a reduction in the percentage of legitimate email that is mistakenly labeled as spam.

Consider an Email Service Provider

Email is a dynamic and complex environment. A good ESP can greatly aid deliverability by providing superior technological capability and know-how, and by continually monitoring, diagnosing and solving deliverability challenges—such as authentication and ISP filtering practices—as they arise. And, because top ESPs oversee deliverability for hundreds of customers, they are able to spot trends much faster than an individual managing email for a single company.

According to eMarketer, this year in the United States, more than 2 trillion emails will be sent--more than 228 million emails every single hour. And, that number is expected to rise to nearly 2.7 trillion by 2007. Technology is making great strides in separating the good email from the bad. But marketers must be aware of these evolving systems to ensure that their email reaches the recipients who are waiting to get it.

For more deliverability tips, download Silverpop's free white paper, "Deliverability: What the Pros Already Know," in this issue of "The Digital Marketer."