How do you guarantee a Millennial will mark your business email as spam?

Include a subject line like this: "Why Hipsters Prefer [Your Brand.]"

Why? For so many reasons.

Let's look at how marketers are self-sabotaging when trying to attract this demographic. And if you're making any of these mistakes, the solutions are all simple fixes.

1. You don't make an appointment with your audience

A shocking 38% of Millennials (born after 1982) are freelancers, meaning that they're not constrained to work exclusively from 9-5.

Of Millennials working regular hours, 89% check their email long after the workday has ended. In other words, Millennials are practicing work-life blending, mixing playtime and worktime, so much that they almost become indistinguishable.

What does that mean for email marketers? Millennials are constantly checking their email, and it doesn't matter whether you're messaging them on their personal or business account.

Content gets quickly marked spam if it's unscheduled. Millennials, who are used to having their emails sold to irrelevant lists, will disregard emails that they didn't ask for.

When you try to sign people up to your email list, guarantee that they will get a consistent email at a specific time. For example, I subscribe to Contently, and I can expect its engaging email every morning before work. Reading those insights is now part of my morning routine.

Promising to deliver at a specific time will heighten your readers' engagement.

2. You don't optimize for mobile

As a generation, Millennials have been trained to be attached to their phones. They were raised with "safety first" in mind—from Baby on Board signs to reforming safety practices in college sports.

Part of staying safe has been remaining in contact with people who can help them out—from Mom and Dad to a designated driver to a boss. Millennials are rarely out of contact with their core group.

Phones are how Millennials stay connected. And though not necessarily checking email because they feel unsafe, Millennials want to have regular access in case they need to be contacted—for their safety or for the safety of their social network.

Expect Millennials to be checking their email at all points during the day on whatever device is most convenient. That means that when their computer screen is off, their phone screen is on. A whopping 70% of consumers will dump email that isn't optimized for mobile—a jarring statistic, given 78% of email is sent without considering mobile platforms.

3. You're writing to Millennials based on stereotypes instead of data

Millennials have been called narcissists, impatient, immature, and entitled, along with a whole gamut of (largely unfounded) slurs.

Think Millennials are selfish? Are you trying to appeal to their so-called "entitlement" instead of sending them cause marketing?

Some 87% of this generation gives to charity and almost half volunteer (more than seven points above any other age bracket). They are notoriously thrifty and, according to Morley Winograd, 85% of Millennials link a worthy cause to their purchasing decisions—and use it as a guide to whether they recommend the brand to their peers.

When you're trying to reach Millennials, rely on data, not stereotypes, to best inform the tone of your email campaigns.

Here are a few hints: A majority of Millennials are not hipsters, they really do love superheroes, and they are just as loyal to their preferred brands as their parents are to their own.

4. You really are sending them spam

Millennials' spam filters are so fine-tuned that they are quick to toss out unwanted emails.

As a generation that grew up learning how to best avoid unwanted online communication, Millennials aren't afraid to dump annoying emails in the spam bin.

Look at your email list. Did your youngest subscribers ask to be a part of your list, or did you buy their email? You should be producing interesting enough content or a product for your base to want to subscribe. If not, you're probably sending irrelevant information to an indifferent audience.

Most importantly, tone down your marketing microphone down to a whisper.

Yes, you should be alerting your email list when you have a sale but also supplying your audience with helpful and practical information. And so long as your content is brief, entertaining, and fresh, Millennials very well might even share it with their friend group.

Trying to attract Millennials with nothing more than a pitch in every email is like trying to crack an egg with a sledgehammer—it's a waste of effort and you end up with a mess.

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Ultimately, Millennials want useful emails. They want the email to work on the device of their choice, they want the email to appeal to their interests and passions, and they want the email to prize helping the reader above the sales call.

If your marketing team is skipping these three simple steps, expect Millennials to label your emails what they are: spam.