1. Check the domain for acceptance policies regarding emails.

UKey Point:
Some domains have limited access to incoming emails due to security verification measures.

2. Adjust your settings to make sure you are using the correct server and protocol (i.e. SMTP, POP, IMAP).

UKey Point:
Check that the appropriate settings are in place to ensure that your email service can communicate with the other domain.

3. Test the connection by sending a test email.

UKey Point:
Use a test email to make sure the connection works properly, including confirming that the email service is not identified as spam.

4. Check your whitelist settings for all incoming email.

UKey Point:
Whitelists ensure that all incoming email addresses are authorized and any potential security issues are mitigated.

5. Review your email server logs for any problems or misconfigured settings.

UKey Point:
Logs contain important data regarding email protocol and can provide diagnostic information to identify any issues with outgoing emails.