One of the most important issues for email marketers is making sure the message makes it to the “inbox” of the intended recipient. An often overlooked key aspect of mailing delivery — in addition to IP reputation — is the actual subject line of the email. Not only does the subject line play an important role in getting delivered, it is imperative to accomplish the main objective of getting your marketing message opened and read by the user and keeping your list active. As such, here are some subject line best practices to follow to ensure your legitimate email is not filtered as spam.

• A subject line should be as short and descriptive as possible. The subject line should be informative and true. If your from name and address are not branded, the subject line should also provide assurance that the email comes from a trusted source. A general rule of thumb is to keep subject lines between 30-50 characters.
• A strong offer can be put right in the subject line. Evaluate your content to understand the likelihood of your message hitting spam filters, particularly if a high percentage of your list is at corporate domains. Corporate domains rely more on phrases or words that have been “tainted” by the spamming community. The major web-based email clients focus on your reputation more than your content.
• The from name and address can be as important as the subject line. A strong offer can be put right in the subject line, but it is important to use punctuation and grammar carefully to ensure that you are not perceived to be a spammer by the receiving ISP.
• The ‘from’ name and subject line should work in tandem. The ‘from’ line should communicate who you are as the sender. Do your best to not change this entry frequently and make it recognizable so that recipients understand that the email was sent by a reliable source.
• If you are cross promoting a sister brand, use the subject line to introduce the sister brand and do not change the ‘from’ address of the originally subscribed-to brand. Any other ‘from’ address is likely to increase complaints. For more information on cross promoting sister brands, please see our recent post on promoting sister brands.

That said, spammers use various tactics to fool people into opening their emails. Spammers often use words that announce a big incentive or urgency. We suggest testing certain keywords or alternative words to optimize your subject lines.

• Some key words and phrases such as “act now,” “trial,” “quote,” and “guarantee” can be tested against “complimentary,” “estimate,” “be our guest,” and “giveaway.”
• While “Free” performs well in subject lines (see Experian CheetahMail’s Free Shipping Report) you might try using “our treat” or “on the house” to see what works best for your brand.
• Avoid excessive punctuation — exclamation points, multiple periods (…), dollar signs ($$), etc.
• In the past putting full words in ALL CAPS was considered equivalent to shouting. Using all caps is a practice used by spammers. Test the use of all caps and monitor any drops in open rates potentially due to filtering.
• Using ‘Re:’ at the beginning of a subject line falsely leads the recipient to think the email is a reply to a previous email. This is a misleading tactic. This tactic is not CAN-SPAM compliant and creates a poor customer experience. If the recipient feels duped into opening an email, you might see an increase in abuse rates or unsubscribe requests.

Just a few little words/phrases in your subject line can make or break the success of your email marketing campaign, not just by impacting open rates but affecting deliverability too. To learn what works best, test. Following these subject line best practices can save your client from losing both excellent reputation and good subscribers.

Subject line testing is not a new concept to email marketing or to this blog. However, it is an important key to email marketing success. Subject line testing is easy to do and offers concrete results, but is often neglected.

Below is a typical inbox. Which subject lines best grab your attention? Which approach would work for your brand? Which one do you think is the worst performing? There’s only way to know – test it out!

Keep in mind:

• Best-in-breed email programs consistently test their subject lines.
• It is important to verify your past findings and current theories about subject lines instead of making assumptions.
• If you can increase your open rates even slightly by optimizing your subject lines, the potential to increase click and transaction rates increases.

Do:

• Be clear and direct.
• Be short – keep subject lines to 50 characters or less. (test this out to make sure shorter is better for your brand)
• Do tell subscribers what’s new in this message.
• Remind subscribers when sales/events are ending.
• Try wistful, fun or emotional subject lines.
• Test personalization, symbols (%, $) and capital letters. Also, I have seen pipes (|) used successfully.
• Set your subscribers’ expectations during the opt-in process about what kinds of emails they’ll be receiving.
• Try incorporating offer codes in the subject line.

Don’t:

• Be deceptive.
• Be too long-winded.
• Deviate from your brand voice too much.
• Scream (use words in all CAPITAL LETTERS).
• Test once and then make long term decisions.
• Be afraid to have fun!
• Don’t confuse newsletters with promotions. If your email is a newsletter, put the name and issue of the newsletter in your subject line. If your email is a special promotion, tell the subscriber what’s inside. Either way, don’t write your subject lines like advertisements.

Subject line recommendations and solutions are not a one size fits all solution. Discover for yourself about what works best for you and what does not work. Don’t forget to document both your testing failures and successes. You do not want to forget what worked and did not work as you perform more tests. Also, you do not want to lose any testing knowledge as employees come and go.

Some subject line testing scenarios include:

• Short versus long.
• Mentioning a product type (shoes, savings accounts, cars, travel destinations).
• Mentioning of brand or style type advertised (Nike, Cargo Pants, Harry Potter, Rolling Stone, Jolly Ranchers).
• Using and testing placement of free shipping, percent-off or discount offers.
• Using language indicating urgency (limited time sale, 3 days only, etc.).
• Using language evoking curiosity or inspiration.
• Using first name personalization
• Including the company name.
• Using capitalization and abbreviations appropriately or intentionally inappropriately (Di$count 4U!).
• Including offer codes in the subject line.

A sample subject line test scenario: The 10-10-80 split

1. 10% of the subscriber list received Subject Line 1.
2. 10% of the subscriber list received Subject Line 2.
3. 80% of the subscriber list received the winning Subject Line.

The winner is most often determined by unique open rate but not necessarily all the time. In the case of including an offer code in the subject line, the winner might be determined by the number of sales generated by that offer code. In this case the subscriber does not even need to open the email for you to make a sale because they can often see the code from the preview pane alone.

If you are having a difficult time deciding what subject lines to create, get inspired by the content of the email or by your web analytics data (to see which content is recently popular on your site and which popular keywords are driving traffic).

When it comes to email marketing, the best subject lines tell what’s inside, and the worst subject lines sell what’s inside. But don’t take my word for it – you need to test, test, test this for yourself.