The best email subject lines are short, descriptive and provide the reader with a reason to explore your message further. Using splashy or cheesy phrases to try to stand out more often results in your email being ignored. In our second email subject line study, MailChimp found that our old recommendation still stands: keep your subject lines simple and to the point.

In this article:

General tips

For this study, MailChimp analyzed the open rates for over 200 million emails. Open rates ranged from an amazing 93% to a dismal 0.5%. Many factors affect how an email is viewed, such as frequency, sender, and the nature of the message. Personal messages are at the top of the interest scale, followed by affiliations and timely news. At the other end of the scale are stale newsletters, requests for money and offers that are too good to be true.

Three Words to Avoid

An unexpected discovery in our analysis was the negative impact of three innocent words. Email marketers are familiar with words such as "free" which are generally to be avoided in emails since they tend to trigger spam filters. We identified innocuous words that won't trigger a spam filter, but will negatively affect your open rates. They are: Help, Percent off, and Reminder.

Localization Helps

Personalization, such as including a recipient's first name or last name, didn't significantly improve open rates. Providing localization however, such as including a city name, did improve open rates.

Newsletter Half Life

Newsletters tend to start with high open rates, but experience some reduction over time. The challenge to the newsletter writer is to keep the content fresh. Repeating the exact same subject line for each newsletter accelerates the drop in open rates. While it is important to establish continuity and branding of the newsletter, ideally each new campaign should provide a clear indication in the subject line of what is inside this newsletter that is of interest.

Subject Line Length

Our analysis confirmed the email marketing rule of thumb, that you should keep your subject line to 50 characters or less. One exception stood out. For campaigns whose subscribers were highly targeted, the readers seemed to appreciate the additional information in the subject line.

The "From:" Line

The "From:" information can be as important as the subject line. As a best practice, the "From:" and subject line should work together. Use the "From:" line to indicate and make clear who you are as the sender. As much as possible, this entry should concisely convey who you are and should remain consistent over time. Save any humorous phrases or concepts for the subject line.

Promotional Emails

By their very nature, promotional emails tend to not perform as well as emails where the reader has a high level of emotional affinity or expects valuable and timely information. Within the category of promotional emails, the same basic rules apply. Keep the message straightforward and avoid using splashy promotional phrases, all capital letters, or exclamation marks in your subject lines. Subject lines framed as questions can often perform better.

List Quality & Frequency

Two additional factors that are difficult to track, but can have a big impact on open rates, are list quality and frequency. When readers know what they're going to receive, they're more likely to open. So these high-quality lists of engaged subscribers tend to see the best open rates. If you start with a good list but send too frequently, open rates drop quickly. 

Subjects with highest open rates

Subject Line Open Rate Comment
Preliminary Floor Plans for Southern Village Neighborhood Circle Members 93% Timely information. Implied benefit for quick action. Over 50 characters in length
Your April Website Stats 92.6% Timely and useful information
Idlewild Camp - Important Travel Information 90.1% Information I need now.
Invitation for Murdoch, Brown, Rove & Johnson's Snow Ball 89.7 Party invitation. Personal and timely
MotorCycling Magazine Reader Survey 88.1% High affinity to activity/experience
Announcing Paige Elizabeth Sullivan 82.6% Birth Announcement: Personal and useful information.
Ship's Log #5: Parus Arrives in Phuket 82.1% Personal and timely
Nautica in Rutland Opens Soon! 79.9% New condos - valuable information to be first in line.
Updated Time Zones & Log On Information 79.1% Required information
MICHAEL DRUCKMAN 1949-2007 77.4% Obituary: Personal
Inside Football: Summer Training Camp Preview Issue 74.3% Timely and useful information

Subjects with lowest open rates

Subject Line Open Rate Comment
Final reminder for complimentary entry to attend the West Freelands BCI Cluster Conference 2006 0.5% Reminder and subject is too long
Tempting August NUSA Specials! 0.9% Special. Exclamation mark
SALE ends soon - up to 50% off all bras at Kara! 1.9% Percent Off
Help Baylor create the ideal college experience 2.5% Help - means ignore
Printers World Offers 100% Commission Up Front 7.5% Too good to be true
3% Commission For You, $10,000 in Upgrades For Your Client 7.8% Bait & Switch
Help Spread The News ! 10.8% Help
Don't Let 2006 Slip Away Without a Tax Deductible Donation To the Children & Families of Omire 11.6% Donation and too long

Avoid repetitive subject lines

It's obvious that if you send the same campaign over and over again (such as reminders for an event), your open rates will decline with each subsequent campaign. But just how much should you expect it to decline? We found one example in our study of a user sending event reminders to his list:

Subject Line Open Rate Comment
Funk n Sandi @ The Roxy on 3 March 8% First Email
Funk 'n' Sandi @ The Roxy on 3 March 6.3% Second Email
This Sat 3 Feb - Funk n Sandi @ The Roxy 5.1% Third Email
Don't forget - Funk 'n' Sandi this Sat 3 Mar! 3.5% Fourth Email

Takeaways

Think about what you expect from other people's email campaigns. What would you like, if you were the recipient? People are flooded with spam and increasingly pressed for time. Vague teasers, constant reminders, and pleas for money are not going to cut through the inbox clutter. The same advice we gave in our previous subject line comparison study remains true. When it comes to subject lines, don't sell what's inside. Tell what's inside.

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