The emails sent could be delivered in spam due to multiple issues such as the mail content(attachments, spam trigger words etc.), domain configurations, domain reputation and more. 

Solution
  • Ensure that the outgoing server and SPF, DKIM, and DMARC records are configured properly.
  • You can check your domain health report here by selecting the option of domain health from the dropdown.
  • Do not use any of the spam trigger words in the content. 
  • Ask the recipient to mark email as not spam, so the domain reputation can improve over time.
  • Use BCC instead of CC


Reference