As mobile has become an increasingly central part of our everyday lives, it’s also become an essential conduit for brands to reach, engage, and retain their customer bases. That’s led a lot of marketers to look beyond email marketing and focus their attention on mobile-first messaging channels like push notifications and in-app messages.

While it’s smart of brands to turn their attention to multichannel messaging in order to better engage their customers, it’d be a mistake to neglect email as part of that transition. While email has a reputation as old-fashioned and desktop-focused, the truth is that it’s not competing with mobile messaging channels—it has become a mobile messaging channel as larger and larger percentages of emails are opened on smartphones and other mobile devices. More than that, it remains one of the most effective ways to reach customers.

But that’s only if you get your email subject lines right. Send a message with a boring, offensive, or bewildering subject line and you’ve lost a big chunk of your recipients right off the bat. Of course, knowing that you need to send emails with great subject lines is a lot easier than doing it all the time.

So, to help you out, we’ve carried out some exceedingly unscientific research on the subject by asking nine Appboy employees to track the emails that they received for a week and then report back on their favorite subject lines—what they were, who sent them, and whether the subject line motivated them to open the email or take action based on its contents.

Here’s what we found:

1. When it comes to email subject lines, retail brands know what they’re doing

While we didn’t set any restrictions on the verticals that could be considered, our respondents overwhelmingly cited subject lines from retail brands as their favorites, with 55% of selected subject lines coming from that vertical. Of the two other verticals that were highlighted, health and fitness brands also performed strongly, with 22% of responses citing them.

2. In general, a great subject line is a short subject line

The average email subject line selected by our respondents was 5.33 words long, suggesting a preference for short and sweet when it comes to making a first impression with email. Some subject lines were even shorter and sweeter—Bespoke Post’s email managed to engage one respondent with a single word—but Slickdeals showed that long subject lines can work, too, with its 12-word behemoth.

3. Don’t assume that recipients are seeing your email right when it’s delivered

Only one-third of respondents saw the email that they cited within an hour of its delivery and another third didn’t see it for at least six hours, suggesting that email may not be the best channel for particularly urgent or time-sensitive outreach. (That would probably be push notifications…) However, every single message was seen within 24 hours of delivery, making it an effective way to reach customers in the medium-term.

4. If people like a subject line, they’re going to open the email (and probably click, too!)

While it makes sense that people would be likely to open the emails associated with their favorite subject line of a given week, it’s still striking that literally 100% of respondents opened the emails they cited. Nearly as impressive, 78% of respondents clicked on a link within the email, suggesting a strong connection between an appealing subject line and a conversion on the part of recipients.

What makes great subject lines great: Appboy employees in their own words

Subject line #1: “Recovery is psychological, as well as physical.”

The respondent: Kevin Ferri, front-end developer

The brand: NYU Langone Medical Center

What made it so appealing: “I recently had surgery and it was a reminder about being careful with my recovery. It gave me tips and things to do to increase my mood during recovery time. The subject line was simple and short, yet packed a lot of meaning. I have had the thought in my head and seeing it in an email made it click. I found it interesting because it was very relatable to me and I could actually use the information they were telling me.”

Subject line #2: “Introducing our new collection!”

The respondent: Kate Tullio, customer support specialist

The brand: IKEA

What made it so appealing: “I really love IKEA and follow their design catalogues readily, so I jumped on the opportunity to see their new furniture collection, which they don’t do often. And once I’d opened the email, I clicked the ‘view the collection’ link because I liked the look of the mugs.”

Subject line #3: “Where the Wild Things Are…”

The respondent: Mike McGowan, training and enablement specialist

The brand: MVMT Watches

What made it so appealing: “The subject of the email differed greatly from the typical ‘Save X% on our products!’ The body of the email was also filled with stunning photographs of the wilderness which evoked feelings of admiration and amazement. But I didn’t click any of the links because I’d actually bought a watch from MVMT a month before and didn’t feel the need to revisit their store.”

Subject line #4: “Find out what your stuff is worth”

The respondent: Kat Sherbo, senior content manager

The brand: Amazon

What made it so appealing: “It promises money, which is always appealing, and there’s an element of mystery. If I want to know how much my stuff is worth, I have to open and read more. It turned out that Amazon was offering a gift card through Amazon Trade-In, which—I gather from the context—is a way for me to sell things I already have back to Amazon. It turns out that I can get $29 for my used items, though I didn’t take them up on it, since they were suggesting selling back an item that I gave as a gift. I would definitely open a similar email in the future, though.”

Subject line #5: “Story On!”

The respondent: Ahmed Gamal, UI/UX designer

The brand: Blurb

What made it so appealing: “That summer trendy vibe that I got from the subject line and from the body copy preview visible in my inbox, which read: ‘Back flips, water fights, cannon balls—the time is ripe for adventure! Keep that summertime state of mind all year long by preserving those good vibes in the pretty pages of a book—Make Your Book.’ It made me think about wanting to print my own Instagram photo book.”

Subject line #6: “☀WEEEEEEEKEEEENNNNNNND FLASH SALE!☀”

The respondent: Mo Khaimov, generalist sourcer

The brand: Blink Fitness

What made it so appealing: “It was very fun and seemed more interesting than the subject lines I usually see. Plus, I was in the market for a gym membership at that time.”

Subject line #7: “What’s Good in Your Hood”

The respondent: Georgia Glanville Harrison, customer success manager

The brand: Class Pass

What made it so appealing: “I liked the subject line and the actual email was really simple and focused on one key task—getting me to search nearby classes. There was a really clear animation of a map come to life inside the email with a single call to action, letting me know that the Class Pass filters make it easy to find local classes. I was curious as to where local classes were, so I clicked.”

Subject line #8: “#Murica”

The respondent: Wayne Egerer, Jr., DevOps engineer

The brand: Bespoke Post

What made it so appealing: “It was a promotional email about items for sale that were “Made in America.” Seeing the subject line, then a picture of an American flag instead of a bunch of items made me interested in clicking to see what the items were.”

Subject line #9: “Amazon Prime Day Deals: $130 Echo, $80 Double Hammock, $112 Grill & More”

The respondent: Bobby DeLorenzo, software engineer

The brand: Slickdeals

What made it so appealing: “It was simple, informative, to the point, and relevant to my interests. They know that I’ve clicked on Amazon deal links previously through them, which makes it relevant. It’s informative because it has sample products and prices right in the subject. It’s to the point because it doesn’t do any of the baity kind of stuff like ‘HUGE SALE LOOK INSIDE’ or ‘Bobby, check out these deals for you!’”

The takeaway

When a brand is looking build a strong, lasting relationship with its audience, one of the most effective things it can do is to provide a brand experience that’s relevant to each one of its customers’ interests and provides real value to every member of their audience.

As it turns out, great emails do the same thing. By hooking recipients with a (usually) brief subject line that intrigues or delights, then providing an email experience that speaks to their interests and tastes, these top-flight emails deepen customer engagement with your brand while helping them fulfil real needs and wants of their own.

Want to take your email outreach to the next level? Check out our piece on mobile email best practices and see how to make them work for you.