So, You hit a Spam folder…
It’s every email sender’s nightmare: your emails end up in the spam folder, not your inbox. But why do emails end up as spam? In this guide, we’ll take a look at the most common reasons legitimate email can end up as spam, and give you the tips you need to avoid ending up in the dreaded spam folder. let’s start.
What is a spam filter (spam folder) and how does it work?
Spam filters are programs designed to identify unwanted or dangerous email so your mailbox provider can prevent them from reaching your inbox. Spam filters use several criteria to analyze email and determine whether a message is spam: Some spam filters rely on a rating mechanism: if an email’s spam score exceeds a certain threshold, the filter marks it as spam. Others use fingerprinting: a method in which spam filters store a collection of known spam and then calculate the likelihood that an incoming email has a similar intent.
Advanced filtering mechanisms also use the power of machine learning to keep an eye on spam. It’s important to know that no spam filter looks the same. Gmail’s spam scoring method differs from Yahoo! Mail’s spam filtering, so it’s possible for your email to end up in one provider’s inbox and another provider’s spam. All spam filters have one thing in common though: They’re set up to ensure that the inbox remains a clean, safe space that provides a great experience for the email recipient.
So when an email—whether that’s personal messages or your brand’s newsletter or transactional email—goes to spam, you’ve done something that caused inbox providers to believe your email is unsolicited or even dangerous, or your email is simply replicating current trends in actual spam.
So what are the factors that tip off spam filters and avoid spam folder?
Let’s break them down one by one:
1. Your email isn’t properly authenticated
It’s surprisingly easy for spammers and phishers to send emails that appear to come from your brand. But here’s the good news: There are a bunch of clever email authentication standards that you can put in place to prevent scammers from using your domain without your permission, and inbox providers rely on these standards to decide which emails are legit (and which are spam.)
So when an inbox provider’s spam filter spots an email that lacks authentication, that raises red flags. In fact, missing or improperly set up authentication is one of the most common reasons why legitimate email gets thrown into the spam folder. So when you’re troubleshooting spam issues, start here:
- Check if you set up SPF (Sender Policy Framework) correctly to provide a public list of sending IPs that are approved to send email from your domain. Here’s our full guide to SPF.
- Are your emails signed using DKIM (DomainKeys Identified Mail), an email security standard designed to make sure messages aren’t altered in transit? Our DKIM guide can give you more details about how it works to secure your email.
- Did you set up DMARC correctly? DMARC allows you to tell inbox providers to quarantine or reject emails that weren’t sent from a trusted source. If you don’t have it set up, scammers might send spam using your domain and hurt your domain reputation (and thus your deliverability). If you set up DMARC but it’s not configured correctly, you might accidentally send your legit email to the spam folder. To avoid these mistakes, learn how to set up DMARC with our ultimate DMARC guide.
2. Your sending IP has a bad reputation
The IP address you use to send your emails plays a crucial role for deliverability. Just like people build up a reputation over time (a good one if you behave like a good human, a bad one if you’re being a jerk) each IP address has a history that mailbox providers keep track of. For example, a track record of low spam complaints and bounce rates makes your sending IP more trustworthy, while a high number of complaints will put a dent in your IP’s credibility.
When you’re sending email via a shared IP, your IP reputation isn’t just built on your sending activity but on the combined sending habits of all senders on your IP. If you’re sharing your IP with spammers, your delivery will suffer. That doesn’t mean a shared IP is a bad thing though: If you’re associated with good senders, that can help boost your deliverability.
3. Your domain has a bad reputation
Just like your sending IP, your domain has a history too—and spam filters are putting more and more weight on domain reputation when scoring your emails. That makes sense: You might be changing email service providers or will use different providers for different types of emails, all of which will use different IPs to send your emails. Your domain, though, is likely the same across providers, so looking at your domain reputation is a clever way to judge your trustworthiness as a sender.
To find out whether a low sending domain reputation could be the reason behind a spam folder placement…
- Check your domain reputation for senders who share the data with you. Gmail’s Postmaster tools, for example, will provide you with a detailed domain reputation score.
- See if your domain is on any blocklists as those have a significant impact on your domain reputation. MXToolBox or multiRBL.valli.org are two popular services to check multiple blocklists at once.
4. Your recipients marked your emails as spam
If recipients mark an email as spam, that’s probably the most straightforward feedback that mailbox providers can consider when judging your emails—so it’s quite certain that users’ spam reports directly impact your deliverability. A high rate of users hitting the spam button will impact your reputation as a sender and cause future emails to land in the spam folder.
Here are a few things you can do to find out if user complaints might be the reason why your emails land in spam:
- Find out how many recipients are marking your emails as spam. If you’re using Google’s Postmaster tools, you can easily see the spam rate (that’s the percentage of emails marked as spam by users vs emails sent to the inbox for active users).
- Register for all available feedback loops, a service provided by some mailbox providers that shares insights about spam complaints generated by your campaigns.
- If you see a spike in complaints, it’s time to investigate: Did a specific campaign cause these complaints? Who are the folks complaining? Did they all come from the same acquisition source?
- Stop sending emails to people who marked your emails as spam. If you continue to send to these folks, that could tank your reputation even further.
5. You don’t keep a clean email list
Spammers and phishers typically don’t have a record of great list keeping. They shamelessly scrape (or steal) email addresses from somewhere, don’t care about invalid email addresses or bounces, and don’t care about engagement as long as a few clueless victims fall for their traps.
If inbox providers assume similar questionable list-building techniques for your brand, they’ll place you into the spam folder as well. That’s why a clean email list is the foundation of healthy email delivery. To keep your email list healthy, follow these tips:
- Only add opted-in subscribers to your list. Adding recipients to your mailing list who never agreed to receive emails from you is a common shortcut to grow your list, but it’s also a path that can lead straight to the spam folder.
- Never ever purchase or borrow email lists. Inbox providers find this practice shady, and they’ll punish senders who send to purchased lists accordingly. The same is true for scraping email addresses from the web. Just don’t do it.
- Remove recipients who unsubscribed and keep a close eye on your email bounces.
- If subscribers aren’t engaging with your emails, remove them from your email list. Inbox providers will notice if a large portion of your subscribers never open your emails or click any links—and it’s not a great look.
6. Your forms are being abused
Form abuse is a surprisingly common reason for spam placements. Spambots sniff out unprotected forms and may submit invalid (or even valid!) email addresses, often causing a great influx of hard bounces and spam complaints that will quickly start to negatively impact your sending reputation. Don’t let that happen.
- Protect your forms with CAPTCHA or set up honeypot fields (i.e. fields that humans don’t see but spambots do) to prevent your forms from being abused.
- Put safeguards in place to detect spam, for example by blocking multiple submissions from the same IP address in a short period of time (those could be spam!)
7. Your content triggered spam filters
For a long time, spam filters heavily relied on content filters. If you were using words or phrases that were commonly used by spammers, that made it more likely that your emails were placed in the spam folder as well.
As spam filters have become smarter and more sophisticated, they rely more and more on factors like your overall sender reputation. But that doesn’t mean that your words don’t matter anymore. Especially when dealing with smaller receivers, including corporate mailboxes or university inboxes, we continue to see a lot of content filtering rules. For example, we’ve even seen mail that includes ‘curse words’ get rejected by university filters for being inappropriate.
If you’re landing in spam and can’t find the cause in your sender reputation, authentication, or other factors listed above, take a look at your content:
- Remove any spammy words or phrases in your email copy, subject line, or preview text.
- Keep your copy concise and meaningful. If you don’t, content filters might mistakenly classify it as “spoetry”, that’s randomly generated copy that spammers use to trick receivers into thinking there’s real content in their emails. Spam filters have become better at spotting this gibberish—but they sometimes generate false positives.
