There is a reason email marketing has been around for so long -- it works, if done correctly. No matter how strong your relationship is with your customers, your emails are still fighting for precious inbox attention. It only takes about three to four seconds for a person to decide whether an email is worth opening, so it’s crucial to capture your receiver’s attention quickly.

Here are nine simple hacks to increase your "open rate":

1. Switch your “from” name.

A small change in the “from” section of an email can go a long way. According to Hubspot, emails sent from a company name have a lower click-through rate compared to emails sent directly from a person. Sending an email from a company spokesperson can increase the probability of your email being opened.

2. Get personal.

Marketing Sherpa did a case study which proved that personalizing emails truly does work. The company tested seven different email campaigns with two different subject lines. The result was that the campaign with the personalized subject line had a 17.36 percent higher average click-through rate.

For example:

Email A: 6 Steps to Building Long-Lasting Client Relationships

Email B: [First name], 6 Steps to Building Long-Lasting Client Relationships

3. Know your length limits.

Emails are viewed in a variety of formats, but as a general rule of thumb, keep the subject line to 50 characters or less. A related issue to be aware of is that many mobile email tools cut off subject lines at 25 characters -- and 66 percent of emails are now opened on mobile devices.

4. Stop using four-letter words.

In the email marketing world, four-letter words like free, help, percent off and reminder tend to trigger a spam filter. Using these words can land your email in junk mail folders instead of inboxes.

5. Use preheader tweaks.

The subject line, and the accompanying text that fills up that line, is known as the preheader. Make sure to keep your subject line to a maximum of 50 characters, to use this space to your advantage. This leaves you with approximately 50 more characters to make a compelling case to your reader by using a call to action to elicit a response.

6. Forget about the “best days/best times” to send emails.

While there is not a single best time to send emails, you can track patterns in customer behavior to identify the optimal times to communicate with customers. This collection of studies shows a few consistent trends. For example, email-open rates tend to drop off on the weekends, not surprisingly. But while emails sent Tuesday through Thursday have the best open-rates, they also compete with the highest volume of emails sent.

7. Make a long-term content investment.

Once you’ve gotten customers to open your emails, it's important to keep their attention. Bad content is one of the top reasons people unsubscribe from 25 percent of emails. Content must be engaging and worth your readers' time. Just because you can get them in the door doesn’t mean that they will stay. Good content leads to brand loyalty and increased referral business.

8. Be negative.

Tabloids do so well because they are the kings of controversy, so don’t be afraid to be a little negative yourself, in your preheader text. For example, we sent this email to a group of newsletter subscribers with two different subject lines. Version B was the clear winner.

Version A: 5 Content Marketing Tips to Help Your Business

Version B: 5 Content Marketing Mistakes (and Why They Hurt Your Business)

9. Use numbered lists.

Numbered lists -- like the one in this post -- catch readers’ attention because it is easy to skim the headers and grasp the content quickly. Our brains are wired to like classification systems. We like knowing the length of something before we begin reading it.

Bringing it all together

While I don’t suggest using all nine of these email hacks at once, I do suggest putting what you’ve learned to the test. These hacks are simply put together to take advantage of how the human brain works. But perhaps the most important tip to keep in mind is to be genuine. Make sure to inject a human quality to your emails so that your customers will always find something to relate to.