12 Reasons Your Emails Are Being Sent to Spam

Boost Inbox Logo Mia Anderson
October 12, 2023

There are several reasons why your emails might be sent to the recipient's spam folder. Email providers use complex algorithms and filters to determine which emails are spam, and these algorithms take into account various factors.

Improving email deliverability is essential to ensure that your emails consistently reach your recipients' inboxes rather than being marked as spam or landing in the junk folder. Here are practical steps to enhance your email deliverability:

What’s Email Deliverability?

Email deliverability is a measure of how successful your email campaigns are at reaching the intended recipients' inboxes, as opposed to being flagged as spam or being diverted to the junk or spam folder. In other words, it refers to the ability of your emails to "deliver" to the main inbox of the recipient rather than being filtered out or treated as unwanted.

Common reasons why your emails might end up in the spam folder:

1. Poor Sender Reputation

If your email domain or IP address has a history of sending spammy emails, it can negatively impact your sender reputation, leading to your emails being flagged as spam.

2. Unverified Sender

Email providers prefer emails from authenticated and verified senders. Make sure your email authentication (SPF, DKIM, and DMARC) is set up correctly.

3. Misleading Subject Lines

Using deceptive or clickbait subject lines can trigger spam filters. Be clear and relevant in your subject lines.

4. Spammy Content

Emails with excessive use of capital letters, exclamation points, or trigger words commonly associated with spam (e.g., "free," "money," "win," "viagra") are more likely to be marked as spam.

5. Low Engagement

If your previous emails received low open rates and few responses, email providers might assume your emails are not valuable to recipients and send them to spam.

6. High Complaint Rates

If recipients mark your emails as spam, it negatively affects your sender reputation. Ensure recipients have a clear and easy way to unsubscribe.

7. Lack of Opt-In

Sending emails to people who haven't explicitly opted in can trigger spam filters. Always use permission-based email marketing.

8. Unformatted HTML

Poorly formatted or overly complex HTML in your emails can trigger spam filters. Stick to clean, well-structured HTML.

9. Missing Unsubscribe Option

Failing to include an unsubscribe link can result in emails being marked as spam. It's also a legal requirement in many places.

10. IP Blacklisting

If your IP address is on a spam blacklist, your emails are more likely to be marked as spam. Regularly check and maintain your IP reputation.

11. Sending Attachments

Attachments, especially large ones or executable files, are often flagged as spam. Avoid sending attachments when possible.

12. Inconsistent Sending Patterns

Sudden changes in your email sending frequency or volume can trigger spam filters. Gradually ramp up your email campaigns if you're sending to a large list.


To improve your email deliverability and reduce the chances of your emails going to spam, it's essential to follow email best practices, maintain a good sender reputation, and regularly monitor your email campaigns for issues. Additionally, you can use BoostInbox to check your emails for potential spam triggers before sending them.

What to read next

Yes, Boost Inbox is designed to cater to businesses of all sizes and industries.

Absolutely! Boost Inbox is compatible with most major email service providers.

The warmup process duration may vary depending on your email volume, but it typically ranges from a few days to a couple of weeks.

Yes, Boost Inbox offers dedicated customer support to assist you throughout the warmup process.

While it's possible, it's best to start the warmup process from the beginning with Boost Inbox for optimal results.