It’s every email marketer’s worst nightmare. They spend days, or even weeks working on a perfect email design, layout, length, and subject line. When they find out from their customer or prospect that the message ended up in their spam folder, it causes extreme frustration.

If you’ve found yourself in this situation, you aren’t alone. Of the billions of emails that are marked as spam on a daily basis, many of them are well-meaning marketers who simply made a few mistakes with their email campaign.

Here are a few of the most common reasons that you are having trouble reaching the inbox of your recipients, and some of the best practices to correct these issues.

You aren’t building email engagement in your subject line

It’s astounding how many marketers are still using the antiquated, “Act Now!” method in their email subject lines. Your subject line shouldn’t be used to express the great savings of your current offer, or how your prospect only has 2 days to purchase before it is lost forever.

Instead, you should be building engagement so that your recipient is interested in what you have to say before they even open the email. Try using your subject line to ask a quick question of your readers, or provide them with a shocking or uncommon statistic to hook their attention and get them to open the message. However, remember to never use an excessive amount of exclamation points or lots of capital letters in your subjects; this is a great way to end up in spam filters. Let your content build excitement, not the punctuation around it.

You are sending messages to stale contacts

Over time, every email list will collect addresses of people who have changed their contact information or are no longer interested in the products, services or information that you have to offer. While you may not think there is any harm in sending messages to these contacts, ISPs will start to notice low engagement rates and will eventually block the IPs that you use to deliver your messages from. To solve this issue, make sure that you periodically take the time to weed inactive addresses out of your list. It doesn’t need to be a frequent undertaking; once every quarter or so is fine, but you still need to ensure that your email list is kept as up to date as possible.

Your Sender/Score Reputation is too low

Sender Score is a service created by data company Return Path that judges how often a specific mail server IP sends spam, gets unsubscribes, or has complaints filed against it. Your Sender/Score reputation is a factor that ISPs use to determine which emails get sent to the spam folder. If your sender/score reputation isn’t where you want it to be, make sure that your send volumes and frequencies are consistent, and try to send more content to the people who actually want to receive it. This will help reduce the frequency with which your emails get marked as spam.

Email marketing is one of the highest-ROI tactics available for digital marketers, but you have to be reaching the inbox for it to be worthwhile. Be certain that you correct these email marketing mistakes if you are making them, so that you can avoid the spam trap and connect with more customers and prospects.