1. Deliverability keeps getting worse

I emailed Forrester analyst Julie Katz to ask her about challenges to email marketing -- and her company's servers bounced back my email. At least the bounce let me know she hadn't received it, so I knew I should call her.

"Deliverability, especially to business addresses, is a challenge," Katz says. "Consumers aren't necessarily checking their spam folders. It requires marketers' constant attention."

That's because the volume of spam continues to break previous records. According to Google's Postini data, in the first quarter of 2009, spam volume grew approximately 1.2 percent per day.

The financial motivation for spammers to outwit ISPs may be greater than the incentive for ISPs to keep up with them, according to George Schlossnagle, president and CEO of Message Systems, a vendor of message management services for email service providers. "A fundamental problem is that email, for most service providers, is a cost center. As the economy gets hard, it's difficult for people to justify putting more money into making those systems aggressively better," he says.

The result is more false positives -- more marketers' emails stuck in spam folders -- and more consumer reluctance to open branded emails. "For email to feel useful, people need for it to be reliable and relatively noise-free," Schlossnagle says.

He advises email marketers to jump through all the hoops to get on ISPs' white lists. "Make sure your DNS works correctly, and they know the mail is coming from you." Email marketers should understand every ISP's both published and unpublished criteria, in order to set up appropriate throttles and rate limits. In this spam-strangled environment, Schlossnagle says, "View email as a living process. It's not set up once, go away, and forget it."