Here are some steps for troubleshooting issues with email delivery to a specific domain in Exchange:

1. Verify that an MX record exists for the domain you are sending to.
2. Check the receiving mail server’s public IP address against any Real-time Blacklists (RBLs)
3. Identify the source of the email in transport logs or message tracking logs.
4. Verify that the Exchange server is not configured to block the source IP directly.
5. Check the domain's SPF records and DKIM keys, if enabled.
6. Configure message authentication using TLS, DKIM, and DMARC configured for the message.
7. Verify the sending domain with Outlook’s SNDS Service.
8. Analyze the connection log to examine the SMTP commands.