This article by MarketingSherpa, which is currently behind a subscription wall, has a couple of very good points I wanted to quote here since most of us won’t be able to access it in full:
“Mistake #2. Not segmenting email lists for tests
Many marketers have large email databases, but don’t know a lot about the records held within. In these cases, they may conduct an email test using their entire database — and create a muddy results picture.
‘Without segmented lists you don’t get good test results,’ says [Corey] Trent [research analyst, MarketingExperiments]. ‘You get all these people responding differently to your emails, which pulls your results in all different directions.’
Spend the time to segment your database and understand the different characteristics of the segments before you embark on email testing. The more you know about unique segments within your database prior to testing, the better chance you’ll have of finding the right messages to appeal to them.
Mistake #3. Stopping tests after one big win
‘With email more than anything, we see people get a big win and stop testing,’ says Trent.
As exciting as those big wins may be, they shouldn’t be the end of your testing process. The makeup of your email lists is constantly changing; external factors, such as the economy, also impact subscriber behavior; and your competitors’ campaigns and tactics are always changing as well.
This constant state of change means you must routinely work on the messaging, layout, calls-to-action and other elements of your email messages to ensure you’re getting the full benefit of a testing program.”