You know it's going to happen eventually: that e-mail subscriber or subscribers that have not clicked on your messages in half a year are going to unsubscribe. If you are a marketer whose revenue model is based on CPM, that is not good.

We spoke with Rhonda Wunderlin, director of Marketing Best Practices and Education at Eloqua to see if there is anything that can be done.

Her advice:

• Everyone should have a program that monitors level of engagement - set the threshold, when you know someone has been sent XX # of emails over XX # of days and they have not clicked through or visited your website, put them into a re-engagement campaign.

• As cliché as it sounds, it really is about sending the right message at the right time - so target your audience with relevant information. "That means moving from a "batch & blast" mentality (same message to everyone in your email database) to a communication strategy that talks to your email recipient about not just what they are interested in, but when they are interested in it."

You may not be able to get there overnight, she says, but you can begin with targeting your communication on demographic data you've captured to ensure the message resonates with "what" a recipient is interested in. "For example, use dynamic content in the e-mail so the value proposition is targeted to based on the recipients title (IT vs. Finance). Serve up a case study that is a success story about another company in that email recipients same industry."

Then, by monitoring their digital body language, you can send a relevant message on a topic you know they are interested in because that individual visited a specific area on your website, she said. Another popular tactic: using automation to trigger a timely email - i.e. they viewed data on Product A, send them an offer for a discount if they buy this week.

Says Wunderlin: In a recent study we conducted looking at over 10,000 months of data from our customers, it is clear that the more targeted the email, (which results in a smaller campaign size) the more the audience was engaged. "When this tactic was used, click-to-open rate increased from an average of 13% to over 60% and bounce back rates were reduced by 50%."

Other tips, she suggests:

• Use surveys as a way to stay in touch - and in return for submitting the survey offer the recipient a copy of the report or the opportunity to see where they stack up against their peers.

• Interactive offers via games or participating in a contest may have less participation than a survey, but those who take the time to participate are truly committed and turn into some of your hottest prospects or most loyal customers.

• Keep the e-mail copy short.

• Link the subject line clearly to a call to action.

• Impose a deadline in the subject line on the call to action.

See other articles in this special report: Tips to Salvage an Unsubscribe; One Final Attempt to Get Them to Re-engage.