Why is my email going to the spam folder?
Few things are more frustrating than sending an important email only to have it disappear into a recipient's spam folder. Email deliverability is a complex ecosystem, but when messages miss the inbox, it is typically due to one of three categories: Authentication, Reputation, or Content.
Understanding how mail providers like Gmail and Outlook filter incoming messages will help you make the necessary adjustments to stay in the inbox.
1. Authentication gaps
Mail servers are inherently suspicious. If they cannot verify that an email truly came from you, they will likely flag it as spam to protect the user.
DKIM (DomainKeys Identified Mail): This is the most critical factor for Postmark users. Without a verified DKIM record, your emails lack a "digital signature." Most major providers now consider unauthenticated mail as high-risk.
SPF (Sender Policy Framework): While Postmark handles SPF for you by default, ensuring your domain’s SPF record is healthy (and not exceeding the 10-lookup limit) is vital.
DMARC Alignment: Providers are increasingly looking for "Alignment." This means your "From" domain matches the domain used in your DKIM and SPF records. Setting up a Custom Return-Path in Postmark is the best way to achieve this.
2. Sender and Domain Reputation
Your "reputation" is a score assigned to your domain and IP address by mailbox providers based on your previous sending behavior.
High Bounce Rates: If you frequently send to invalid or "dead" email addresses, providers assume you are using an old or unverified list, which is a hallmark of a spammer.
Spam Complaints: When a user clicks "Report Spam," it is a heavy blow to your reputation. If your complaint rate exceeds 0.1% (1 complaint per 1,000 emails), you will likely see a drop in deliverability.
Shared vs. Dedicated IPs: Postmark uses highly vetted shared IP pools to ensure great reputation for everyone. However, if you are a very high-volume sender (over 300k emails per month), a Dedicated IP might be necessary to isolate your reputation from others.
3. Content Triggers
Modern spam filters use machine learning to scan the actual content of your email. While "spammy words" are less of a factor than they used to be, specific technical content issues still trigger red flags.
URL Shorteners: Spammers frequently use services like bit.ly to hide malicious destinations. Use full, branded links instead.
Poor HTML Structure: Broken tags, missing
<body>tags, or using only an image with no text can look like a trick to bypass filters.Subject Line "Gimmicks": Excessive use of caps (URGENT!!!), too many emojis, or misleading subject lines that don't match the body content can trigger filters.
Missing Unsubscribe Links: For any non-transactional mail (broadcasts/newsletters), a clear, functional unsubscribe link is legally required and essential for inbox placement.
How to diagnose the issue
If you suspect your mail is going to spam, follow these steps:
Check your Postmark Dashboard: Look at your Statistics tab. Are you seeing an unusual number of "Bounces" or "Spam Complaints"?
Verify Authentication: Go to Sender Signatures and ensure DKIM and Return-Path show as "Verified" with a green checkmark.
Use a Seed List: Send a test email to a few different providers (a personal Gmail, a Yahoo account, and a corporate Outlook account). This helps you see if the problem is localized to one specific provider.
Test with Mail-Tester: Use a tool like Mail-Tester to get a comprehensive score on your email’s "spamminess," including authentication checks and content analysis.
A note on "Warm-up" If you are moving a high volume of mail to a new domain or a new service like Postmark, don't send it all at once. Gradually increasing your volume over a week or two allows providers to "get to know" your new sending pattern, which prevents sudden spam filtering.
For a deeper dive into maintaining a healthy sender reputation, visit our deliverability guide: https://postmarkapp.com/glossary/email-deliverability