How Subject Lines Affect Deliverability

How Subject Lines Affect Deliverability

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.