Rule 3: Don't forget segmentation.

It's important to test which groups respond to which promotions and adjust your email campaigns appropriately. After all, you don't want to waste your least-profitable offers on fanatics who will respond to deals that are more lucrative from the brand's perspective.

After a publishing email marketer identified its "fanatic" and "frequent" responder tiers, it decided to deliver increasingly attractive offers over time. After all, the fanatics tend to convert on the most client-profitable offers, the frequents on the slightly less profitable offers, and so on. By continuing to invite lower-tier responders and non-responders from earlier touches into the stream over time, a marketer can maximize its overall conversion rate. Thus, never send email without at least two segmented offers (at the very least, for testing purposes).

Rule 4: Don't overcomplicate.

Managing more than three to five segmented offers can often be more trouble than it's worth. For example, a clothing retailer decided to manage a source-specific opt-in program across hundreds of partner programs and sites. Creative for each and every welcome email and landing page was custom tailored to each partner and website. As you can imagine, this effort required significant man hours.

On the surface, it seemed logical that effective on-boarding required such one-to-one attention. However, after analysis and testing, the 80/20 rule showed its ubiquitous face again. Most opt-in sources converted just as effectively when greeted by the clothier's branding compared with a partner's custom-tailored look and feel. Only a handful of the opt-in sources saw less effective conversion rates when switched to the client's creative. In short, the clothing retailer could have saved untold creative resources by injecting more standardization into its welcome emails and landing pages.

Moving forward, new opt-in partners can be vetted against the on-boarding benchmarks established by the generic versus custom test. If a new partner doesn't convert well on generic creative, they can be dropped. If they convert very well, the retailer can assess whether they might do even better with the custom treatment. The takeaway lesson is that you need to be sure you know the ROI for your segmentation efforts.