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Best Practices in Writing Email Subject Lines

2007 Subject Line Comparisons

The best email subject lines are short, descriptive, and provide the reader with a reason to explore your message further. Attempts to stand out in the inbox by using splashy or cheesy phrases will invariably result in your email being ignored. In short, the conclusion of i-Emailer's second email subject line study echoes our previous study - keep your subject lines simple and to the point.

For this study, i-Emailer analyzed the open rates for over 200 million emails. Open rates ranged from an amazing 93% to a dismal 0.5%. Many additional 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. Read more about the three words to avoid in email.

Localization Helps
Another finding: personalization such as including a recipient's first name or last name does not significantly improve open rates. Providing localization, such as including a city name, does help.

Newsletter Half Life
Newsletters tend to start with high open rates, but all experience some reduction in 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
The general rule of thumb in email marketing is to keep your subject line to 50 characters or less. Our analysis found this to generally be the rule. The exception was for highly targeted audiences where the reader apparently appreciated 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 in tandem. The From line should communicate who you are as the sender. As much as possible this entry should not change and should concisely convey who you are. 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, CAPS, 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. Email marketers that build high-quality lists where readers know what they are going to receive enjoy the best open rates. If you start with a good list but send too frequently, open rates drop precipitously.

Best & Worst Subject Line Examples

Here's a comparison of email campaigns taken from the highest vs. the lowest open rate samples in our study.

Note: all names have been changed in the subject lines below.

Subject Lines With Top Open Rates
Subject LineOpen RateComment
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 Information90.1%Information I need now.
Invitation for Murdoch, Brown, Rove & Johnson's Snow Ball89.7Party invitation. Personal and timely
MotorCycling Magazine Reader Survey88.1%High affinity to activity/experience
Announcing Paige Elizabeth Sullivan82.6%Birth Announcement: Personal and useful information.
Ship's Log #5: Parus Arrives in Phuket82.1%Personal and timely
Nautica in Rutland Opens Soon!79.9%New condos - valuable information to be first in line.
Updated Time Zones & Log On Information79.1%Required information
MICHAEL DRUCKMAN 1949-200777.4%Obiturary: Personal
Inside Football: Summer Training Camp Preview Issue74.3%Timely and useful information

Subject Lines With Low Open Rates
Subject LineOpen RateComment
Final reminder for complimentary entry to attend the West Freelands BCI Cluster Conference 20060.5%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 experience2.5%Help - means ignore
Printers World Offers 100% Commission Up Front7.5%Too good to be true
3% Commission For You, $10,000 in Upgrades For Your Client7.8%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 Omire11.6%Donation and too long

Reduce Opens with Repeating/Reminder 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 LineOpen RateComment
Funk n Sandi @ The Roxy on 3 March8%First Email
Funk 'n' Sandi @ The Roxy on 3 March6.3%Second Email
This Sat 3 Feb - Funk n Sandi @ The Roxy5.1%Third Email
Don't forget - Funk 'n' Sandi this Sat 3 Mar!3.5%Fourth Email


Put yourself in your recipients' shoes. 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 2006 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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