Why do the messages sent through Mailgun to approved receivers get classified as spam in Gmail?

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There are various reasons why emails sent through Mailgun might be marked as spam in Gmail. Some of the common reasons are:

1. Content: If the content of the email includes certain keywords or phrases that commonly appear in spam emails, it could result in the email being classified as spam.

2. Sender reputation: The sender's reputation plays a significant role in determining whether an email will be marked as spam or not. If the sender has a poor reputation, it could increase the likelihood of their messages being marked as spam.

3. Email authentication: If the email is not authenticated properly, Gmail may interpret it as a spam attempt and filter it out.

4. User behavior: Gmail is designed to learn from a user's behavior, including whether they mark emails from a certain sender as spam. If enough users mark emails from a sender as spam, it could result in all emails from that sender being sent to spam.

To prevent Mailgun emails from being marked as spam in Gmail, it is important to follow best practices for email marketing and ensure that the content, sender reputation, and email authentication are all optimized.