Button vs. text link:
Which draws more attention? With potentially more than half of your subscribers reading messages with images off, they might be missing your call to action or link to your offer. Send one message with a button image, optimized with an action tied to the offer, to half your list. Send another message with a text link to the other half and compare results. Remember, instead of using a generic message like "click here" on the button image or text link, use a specific call to action like "buy now" or "get the details" or "save 20% now."
HTML button vs. image button:
Some people cal it the "bullet proof button" but we call it a requirement. You can use simple HTML tactics, such as background colors, text and small images, to create a very close-to-image-based button. The major difference: with images turned off, readers can still see your button and know where to click.
"Yes" and "No" buttons on reactivation emails:
These go out to subscribers who haven't acted on your emails in a set amount of time (one year or longer, for example). Providing readers with a clear choice inspires action, and doesn't leave readers who meant "no" hanging on hopes you'll notice their silence. Whether they return to active status or leave the list, either is better than being a black hole on your list or a potential spam complainer.
Navigation bar vs. no navigation bar:
Does a navigation bar (which can replicate your Web navigation bar or move readers farther down inside a longer message) justify the amount of message real estate it consumes? Drop it out next time and see if that affects Web traffic or clicks.
Call to action or offer in snippet text vs. standard administrative text:
This puts your key information in the first line of text that appears in the email message and can also be seen in the inboxes of some Web email clients such as Gmail. (Also, see "Web-version link" below.)
Text vs. HTML:
The oldest debate in email design flares up again because of mobile users, whose smartphones might mangle your HTML message. Send a text-only message to a small group or reformat your existing text message to appeal to mobile users.
Administrative copy on the side vs. at the bottom:
Multiple vs. single images:
For this test, do the opposite of your current design. If you use a single large product image, switch to two or three smaller ones: side view, close-up or in use, for example. Swapping out a single large image for smaller ones could reduce your image-to-text ratio, which could help deliverability, too, because a high image ratio can trigger spam filters.
2. Link usage and placement
Unsubscribe at top and bottom vs. bottom only:
This could help reduce spam complaints. You aren't encouraging people to opt out of your list. You're simply making it easier for those who do want to leave. They might overlook a bottom-only link and go for the spam button only because it's more convenient.
Web version at bottom, mid-copy or side vs. top only:
The top line is your prime real estate and could be used more effectively for some other purpose. (See "snippet text" above.) Try moving your Web version link around to see if you can make better use of the top portion of your message.
More links vs. fewer links:
We assume more links are better because it gives the reader more access to your Web site and more chances to find something to buy. This can backfire for mobile users, however, especially when you link headlines, body copy and calls to action in one short paragraph. Reduce the links to the most essential call to action. Or, add more links to see if that does bring more shoppers to the site.
Specific vs. general subject line:
Put the call to action, lead promotion or main newsletter topic in the subject line instead of the general newsletter name or a hint at the contents. ("$50 off your first purchase" vs. "Weekly offer from Big Department Store" or "See our latest deal inside!")
Longer vs. shorter subject line:
Some research suggests longer subject lines deliver shoppers who are most likely to buy. Try adding one more feature to the subject line, making sure the most important words still appear first ("20% off Outlet deals plus free shipping" vs. "20% off Outlet deals").
Longer vs. shorter copy:
Ad copywriters will debate this forever, but what appeals to your subscribers? Create one message with a longer or shorter product description than you usually use.
Actionable alt text vs. no alt text or simple descriptions:
Alt text appears when images are blocked and consists of words that describe an HTML image. Add descriptive copy or calls to action here instead of placeholder copy like "product_image_one."
Cash offer vs. percentage-off offer:
If you usually offer a percentage discount, try specifying a monetary amount to catch more attention.
More/fewer offers vs. fewer/more offers per message:
If you typically list only one offer, add an alternative to entice shoppers who don't want your primary offer. Conversely, if you send three or more offers per email, sharpen the focus. Be sure the subject line reflects this change.
Message Frequency and Timing
This can be a tricky area, because increasing frequency can also increase spam complaints and unsubscribes. Never boost frequency, especially during the heavy holiday-shopping season, without testing it first and then watching delivery reports, unsubscribes, inbound email and ISP feedback loops for subscriber backlash.
Regular sending time vs. time most often opened:
You could be hitting more shoppers when they are ready to deal with your email. Note: open rates don't tell the whole story. Some readers are opening your messages but not recording an open because they are reading it with images off or on mobiles.
Regular sending day vs. highest-open day:
Same principle as shifting time of send, and with the same caution on the open rate itself.
Trigger-based email vs. broadcast:
Create a special offer for people who didn't open or click on links in your last message. Anyone who did open or click would receive your regular offer or newsletter.
Add a less-frequent daughter list:
This list bundles all the content you send out daily or multiple times a week into a single weekly package.
Add a mid-cycle message on lists that mail biweekly or less frequently:
Proceed carefully here to avoid the higher-frequency risks, and make sure the message maintains the focus of your regular list.
This area goes outside the message itself to bring in more motivated subscribers and to better engage them once they sign up.
New/redesigned welcome message vs. no message:
Send a beefed-up welcome message to half of your new subscribers and either the same message you sent before, or nothing if you don't use a welcome message.
Features/benefits-based opt-in invitation vs. action-only invitation:
This covers the language you use to promote your email program. "Sign up for email offers here" is action-based. "Get email-only special offers and news here" is feature- or benefit-based.
Add a new delivery channel:
Add an RSS channel to deliver your email messages. Also, some email marketers now include links that allow users to post messages to their profiles in several social networks, including Facebook, Digg and StumbleUpon. Check your web analytics to see if these new channels move the needle on list growth or conversions.