Like most other forms of marketing, e-mail marketing is more art than exact science. However, certain elements can be tested and measured to improve your e-mail marketing success. So let's take a look at the three key variables that can profoundly impact your results.

1. Test by delivery day and time.
The ideal time to send your e-mail marketing communication depends on who your customers are. If you're e-mailing to a business list, you may best get their attention if you send on Tuesday, Wednesday or Thursday from 10 a.m. to 2 p.m. Generally, Mondays aren't a good day to send, as spam has flooded in over the weekend and your legitimate e-mail marketing might get overlooked or deleted. First thing in the morning, at the end of the day and Fridays aren't great either, as desk jockeys are eager to either get to work or get out of work. Try midweek, midday, and see if that improves your open rate.

If your business targets a large percentage of consumers using personal e-mail addresses, try sending after 6 p.m. or on Saturday, when people are home from work. Experiment to find out what works best for your business and your audience.

2. Test your subject line.
Your e-mail marketing communication competes with personal e-mail, work e-mail, other commercial offers and all the other messages that clutter our collective inboxes. A well-written subject line that tells readers what they can expect if they open your e-mail is absolutely essential. Otherwise, you're destined for the delete heap. Write a teaser with an interesting tidbit that entices readers to open your e-mail and learn more. Here are a few examples:

Boring : "Our Monthly Tax Newsletter"
Better : "3 Tax Tips You Need to Know"

Boring : "Fall Fashions In Stock"
Better : "How to Pick Jeans That Fit Right (Not Tight)"

If you're advertising a promotional campaign, try creating a sense of urgency: "15 Percent Off--This Weekend Only," or "Free Shipping Until Midnight Tonight." To test this variable, try writing two subject lines for the same campaign and sending the e-mails to two different groups. Then examine your e-mail tracking and reporting data to see which one got better results.

3. Test your e-mail offer and call to action.
How clear is your e-mail's call to action? Where on the page is it placed? If it's drowned out by too many graphics or buried at the bottom of the page, your reader may likely miss it. Be clear on what you're asking the recipient to do, and position that call to action prominently--whether it's to click for more information, download a free report, sign up for a free consultation or order your product. Here are some helpful hints:

  • Make sure your call to action is visible in the preview window.
  • Try experimenting with placing your call to action at the top of your page and on the side (or again at the bottom). You might catch the attention of readers who missed your offer the first time they scanned the page.
  • If you're sending out plain-text newsletters, try moving up to an HTML template with a few well-placed graphics or photos to make your communications more visually inviting.
  • If you're currently sending out promotions regarding 10 or more different items, try cutting that down to just two or three. Include a link to your catalog so readers know what else you have to offer.

You don't have to risk your entire campaign trying out new tactics. Test these variables on a segment of your e-mail marketing list, but make sure it's large enough to create meaningful, measurable results. Shoot for at least 100 test recipients, make the sampling as random as possible, and watch your tracking reports for changes. (Learn more about interpreting reporting data here .)

Learning by trial and error lets you fine-tune your e-mail marketing campaigns so you can raise your customer response rates and ultimately bring in more business. So to find what works best for your business, test, test . . . and test again.