Here are a few steps to troubleshoot why emails aren’t sending to all recipients:

1. Check if the email address is in the correct format.
2. Verify if the email address is in the recipient’s contact list.
3. Check any email filters that may be blocking the email.
4. Ensure that the email is meeting the system repeat sending limits.
5. Check for any duplicate emails in the recipient address list.
6. Check if the email is blocked by any third-party anti-spam systems.