Email deliverability refers to the ability of your emails to reach the inbox instead of the spam or junk folder. Deliverability is determined by how receiving email servers evaluate your emails based on technical setup, sender reputation, recipient engagement, and email content. Improving deliverability means consistently optimizing these factors so your emails are recognized as wanted and trustworthy.
What is email deliverability and how does it work?
Email deliverability describes whether your emails successfully arrive in the inbox of your recipients. Receiving email servers use filtering systems to determine if an email is relevant and safe.
These systems evaluate multiple factors simultaneously, including authentication settings, sending behavior, recipient interaction, and message content. Because these filtering mechanisms are not transparent, there is no single cause or guaranteed solution for deliverability issues.
On this page, the following topics are covered:
- Why do emails end up in spam?
- How can you check your sender reputation?
- Why do emails to Outlook or Hotmail go to spam?
- How can you improve your email deliverability?
- Why do emails end up in your own spam folder?
- Frequently asked questions
Why do emails end up in spam?
Emails end up in spam when receiving email servers classify them as unwanted or suspicious. This classification is based on a combination of signals rather than a single rule.
- Email content contains characteristics commonly associated with spam
- Recipients did not explicitly opt in to receive emails
- Low engagement, such as limited opens or clicks
- Missing or incorrect technical configuration
- Irregular sending patterns or sudden volume spikes
Important to know
Receiving email providers do not share the exact reason why an email is placed in spam. Improving deliverability requires consistent optimization across multiple factors.
How can you check your sender reputation?
Sender reputation reflects how trustworthy your emails are perceived by receiving servers. A lower reputation increases the likelihood of emails being filtered as spam.
You can monitor your reputation using external tools such as Sender Score.
Some email providers also use additional metrics:
- SCL (Spam Confidence Level)
- BCL (Bulk Complaint Level)
These values can typically be found in delivery reports and provide insight into how your messages are evaluated.
External tools
Tools such as Sender Score and Analyze.email can help identify potential deliverability issues before or after sending.
Why do emails to Outlook or Hotmail go to spam?
Emails sent to Outlook or Hotmail addresses may be filtered to spam or quarantine when the assigned SCL or BCL score is too high. These scores are influenced by recipient behavior, such as marking emails as spam or ignoring them.
There is no single fix for this behavior, but the following actions can help improve placement:
- Encourage recipients to mark emails as “not spam”
- Ask administrators to submit false positives for review
Important
If emails are incorrectly classified as spam, administrators can submit them as false positives through Microsoft review processes to improve future filtering decisions.
How can you improve your email deliverability?
- Ensure DKIM, SPF, and DMARC are properly configured
- Keep DNS records active
- Use a consistent sender name and sending domain
- Monitor your sender reputation regularly
- Review SCL and BCL scores where available
- Test campaigns before sending
- Use internal tools or external spam checkers
- Keep sending volume consistent
- Avoid sudden spikes in volume
- Gradually increase volume for new domains or IPs
- Send relevant and personalized content
- Maintain a balanced ratio between text and images
- Avoid excessive use of spam-like wording
- Avoid ALL CAPS and excessive punctuation
- Avoid unsupported elements such as scripts
- Limit the use of attachments
- Keep emails concise and easy to read
- Send emails only to recipients who have opted in
- Keep contact lists clean and up to date
- Process bounces and remove invalid addresses
- Reduce or stop sending to inactive contacts
- Include a clear and accessible unsubscribe option
- Encourage recipients to add you to their address book
- Ask recipients to mark emails as “not spam” when needed
Why do emails end up in your own spam folder?
Emails may appear in the spam folder of your own organization when internal mail servers treat messages sent from your own domain as suspicious.
This can occur when external sending systems use your domain as the sender. In these cases, administrators can allowlist the sending IP addresses used for delivery.
Frequently asked questions
Why are my open rates decreasing?
A decrease in open rates can indicate lower engagement or that emails are being filtered into spam instead of reaching the inbox.
What should I do if my emails go to spam?
Review your technical configuration, improve your content, clean your contact lists, and monitor your sender reputation consistently.
Can deliverability issues be resolved immediately?
No, deliverability improves over time through consistent sending behavior and positive recipient engagement.
Is inbox placement guaranteed?
No, inbox placement depends on how receiving email servers evaluate your emails and how recipients interact with them.