Summary: Focus on the first 40 characters. Descriptive and well-written subject lines allow recipients to make an informed decision to get more details or move on.

Email newsletters, marketing campaigns, and email blasts live or die in the crowded inbox, with survival determined mainly by users’ scanning and assessment of sender information and subject lines.

Satisfied users are those that are confident about their decision to open an email or bypass it. Clear, recognizable sender information and a well-written, descriptive subject line give users the information that they need to make an informed decision.

Based on our user research with hundreds of emails, these 5 guidelines for subject lines will increase the chance that your message will be one of the few to survive users’ ruthless pruning of their overloaded mail stream.

1. Include content in the subject line.

Users prefer straightforward subject lines that accurately tell them about the newsletter’s content. They value descriptive headlines over those that state the name of the email newsletter or the month or day it was written.

For example, a user in our study received a Word of the Day newsletter, which included the featured word in the subject line. The subject line was:

dyad: Dictionary.com Word of the Day

The recipient said, “One thing that’s good about it is that they list the word itself in the subject line, so if I see that and realize it’s a neat word, I will open the email instead of deleting it immediately.”

It might be tempting to think that a generic subject line will entice users to open a message to see its content. After all, if users can see the content in the subject line and determine they’re not interested, they won’t open the message. However, it’s much better to inform the user and let them decide than to require them to open a message to find out that they’re not interested in it. Many people may not bother at all and simply delete it instead.

For example, the subject line of an email sent from The Leukemia and Lymphoma Society was:

April 2014 eNewsline

This subject line didn’t include any details about the contents of the message. In order to get any information, the user must open the message. The interaction cost is high, and the benefit is unknown or vague at best. Over time, users may not have the time or desire to open the message each time they receive an email from the organization.

Remember that email is a relationship tool. It’s the best and most cost-effective way to keep in touch with customers over time. Increase the perceived value of a subscription by reducing the likelihood that subscribers suffer the penalty of opening messages they don’t like.

2. Front-load the subject line with keywords and limit it to 40 characters.

Email programs limit the number of visible subject-line characters in the inbox view. These limits range widely from program to program and change over time. Although we recommend displaying no more than 40 characters in the subject line, many email programs display far fewer than that.

Necessary content should be at the beginning of the subject line so it doesn’t get cut off. Even if a full subject line is visible to users, they often read only the first few words of a subject line. Information-carrying, enticing, descriptive words should be used first in the subject line.

For example, a message sent from an entertainment venue, Merrill Auditorium, had the following subject line:

Merrill Monthly Newsletter: Berinsten, Bobby McFerrin and... Bear Hunts!

The first 3 words of the subject line are the same for each monthly newsletter, so users must scan past them to find meaningful and unique information. It would be best to remove those 3 words from the subject line and start with the names of the featured performances.

3. Don’t repeat sender information in the subject line.

Users want to be able to identify a newsletter and know what it’s about with a quick glance at the subject and sender. Newsletters only have a limited amount of space to inform users. Repeated information is a waste of space.

For years, messages sent from dailypuppy.com used DailyPuppy as the sender information and the same subject line for each newsletter:

The DailyPuppy | Pictures of Puppies

The repetitive words used in the sender information and subject line provided no information about the featured puppy. Users had to open the message to see the details. It would have been better to put the featured dog breed in the subject line instead.

Daily Puppy recently changed its subject lines to include the name and breed of the featured puppy. For example, a recent subject line was:

Meet Pistachio the English Bulldog!

This is much more descriptive and doesn’t repeat details provided in the sender information.

4. Avoid using recipients’ names in the subject line.

Some newsletter subject lines include the recipients’ name. Users are wary of these messages, because they know the emails aren’t written specifically for them; they realize that they are one of thousands of people receiving the same message. In most cases, the use of the recipient’s name in the subject line is unnecessary. Including another meaningful or descriptive word is a better use of the space.

Users are especially sensitive to messages that included their name in all capital letters, especially when the rest of the subject line was in sentence case or title case. For example, the sender information for a message from Toys“R”Us included the recipient’s name in capital letters.

If names must be used in the subject line:

Only use the recipients’ first names.

Capitalize the first letter of the name only.

Avoid placing the recipients’ name as the first word in the subject line, because users will need to scan past it to see anything meaningful or unique.

5. Be cautious with symbols and special characters.

The use of hearts, stars and other symbols and special characters is intended to draw attention to individual emails in a crowded inbox. However, this makes the message feel much more like “marketese” and not directed to the individual.

Some email clients may not display these symbols and special characters appropriately. If special characters or symbols are insisted, test the newsletter on a variety of email clients and make sure it displays properly.

If special characters must be used, don’t use them at the beginning of the subject line. Instead, place them at the end or the middle of the line so users can scan meaningful words first—not a symbol.

For example, Staples put a sun symbol at the beginning of the subject line. Users must scan past it to see anything meaningful. The Home Depot does a better job by putting the two star symbols further into the subject line.

Instead of symbols and special characters, use the allotted space for meaningful, compelling keywords to make the subject line more personally relevant to your subscribers.

Take Advantage of Every Character in the Subject Line

Organizations that send email messages have a limited number of characters to work with, so each character in the sender information and subject line should be used wisely. This is often the only information that a user has when deciding whether or not to open a message.

For additional guidelines on email newsletters, please see our Email Newsletter Design report, which includes 211 guidelines for newsletter subscription, content, and account maintenance.