Go for Seconds If at first they don't respond, send, send again.

Timing is everything, as D.J. Waldow knows more than most. As an account manager with e-mail marketing firm Bronto Software Inc., Waldow noticed that the companies he worked with would send out e-mail blasts and get open rates of 15 percent to 20 percent, even for targeted, opt-in lists. It just didn't seem like enough.

"How many times do you get an e-mail [and] you're on the phone or you're busy and can't open it, even if it's relevant," Waldow says. "I started to think, what if we send that message again, as a re-mail? We could alter the subject line and change the content a bit and increase our open rate."

Michael Bisbee and Michael Kaulentis, both 31, are avid users of e-mail for their business, MK Biz LLC, a $6 million company that operates Chicago nightclubs Manor and RiNo. E-mail marketing is essential for telling their young, tech-savvy clients about the latest events and happenings at their clubs. However, with at least one e-mail going out per week, Bisbee says, "We don't want them to feel overwhelmed or annoyed. E-mail marketing [especially in the nightlife industry] can be a very delicate balance between good coverage and overexposure."

Waldow has noticed some re-mailing best practices, which he and his colleagues captured in a free white paper titled, "Re-Mailing: Targeting Those That Don't Open." Among the recommended tips are: Time your re-mails. It's easy to overdo re-mailing, so some good rules of thumb are to resend one week after a monthly mailing or five days to a week after a semimonthly mailing. If you mail once a week or more, try resending only to those who haven't opened the last three or four e-mails.

Change the content. Write a new subject line and change the look of the e-mail. That way, it will look fresh if someone caught sight of it before deleting. Focus on benefits to the customer in the subject line and give some sense of urgency. Waldow suggests including a time-sensitive promotion or some type of exclusivity, such as "for subscribers only."

Test yourself. Testing is the best way to determine what works with your customer base, says Waldow. Go back to subsets that didn't respond to one offer and try a different offer. The best e-mail marketers segment their lists and target promotions that work specifically for their audience segments.

Gwen Moran is co-author of The Complete Idiot's Guide to Business Plans. Reach her atgwen@gwenmoran.com.