"If they don't open it, why even bother sending it?" So goes the mantra of email marketing. If you optimize your subject line strategy, you'll optimize your open-rate. If you optimize your open-rate, you'll optimize your email program. In this section, we'll discuss about various subject line tests.

Why Use Subject Line Test?

There are only two things that determine the open-rate of your email. While brand equity and user quality play a role, at the end of the day it's whether your email gets delivered into the inbox and the quality of your subject line that drive email opens. While brand equity and user quality take a significant time to build and inbox deliverability is a science and an art in its own form, you can control it easily with some simple subject line tests. Mastering the best subject lines for your email marketing program is step one in getting the maximum number of views to your email campaign.

Types of Subject Line Test

Below are some common and useful subject line tests that you may want to consider for your email program.

Personalization: As we've previously discussed, many case studies reveal that using email personalization, such as a recipient's first name or user name, can dramatically improve email open rate. This may or may not be true for your email list – or it may only be true for a segment of your email list. Be sure to test all versions: non-personalized, personalized with a name, or personalized with a user name to see if you see a shift in user response.

Specific or Vague: Sometimes, a subject line that doesn't quite tell you what will be inside the email causes curiosity and therefore users open the email. Sometimes, however, telling users exactly what they'll be getting inside of the email works better. Both variations are worth testing to see what your users will respond to most effectively.

Mention the Offer: In many cases, if you are including an offer or discount in your email campaign, mentioning the specifics of the offer in the subject line can increase open rates. However, don't fall into the "Groupon" effect. If you're always promising big offers in your subject line, then your users will come to expect those big offers and not open anything that doesn't mention them. Test mentioning offers, but never rely solely on those offers for ongoing open rates.

Different Offers: The subject line is a great place to test different offers against each other. Does a free shipping subject line get a better response than a fifty percent discount offer? While testing offers against each other is a multi-step process, the subject line is probably the best place to get instant feedback on what offers your users are most interested in.

Short Versus Long: While a longer subject line may be a spam or delivery problem, a shorter one may not give users enough information. Test short form versus longer subject lines to see if they make a difference.

Dated or Time Sensitive: Sometimes, a little urgency can go a long way and telling users that an offer is for a limited time or giving a cut off time for action will increase your open rates. However, sometimes your users are longer-tail users and urgency simply makes them think that the email was already out-of-date by the time they considered opening it. Try both versions and see if your users can be spurred to action by a time frame or if you need to allow them their own leisure time to open.

Best Practices for Subject Line Tests

As always, be sure that your A/B list split is clean. This is particularly true of subject line tests. If you have an uneven balance of user states or email service providers, you're incredibly likely to have invalid open rate data at the end of the day.

Test subject line concepts over several sends. Even if you are incredibly cautious about the quality of your A/B split, there are still factors that you won't be able to account for such as long-tail opens and possible timing issues. In general, run your subject line tests for three to five times before determining what the data means.

Be aware of inbox deliverability! Your subject line can have the greatest impact on your ability to get into the inbox instead of the spam or junk folder. If you're running a subject line test of multiple subject line concepts, be sure to always check deliverability before you send to your list.

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