[Email Security] Describe valid submission

src/content/docs/cloudflare-one/email-security/email-monitoring/search-email.mdx

@@ -160,6 +160,22 @@ To escalate a reclassification:
 2. Select the three dots > select **Escalate**.
 3. The dashboard will display a message to authorize escalation. Select **Escalate**.
 
+### Invalid submissions
+
+A submission is invalid when:
+
+- A submission has no .EML file attached.
+- A submission has been made with an incorrect file extension.
+- You did not configure the domain you are submitting emails for. 
+- A policy has been enforced that causes an email to be received or blocked.
+- A submission was made to the wrong team or user alias.
+
+To ensure your submission is valid:
+
+- Ensure your submission has a file attached and the file has a .EML extension.
+- Ensure you configure the domain you are submitting emails for.
+- Ensure policies are configured correctly.
+
 ## Move messages
 
 Moving messages allows you to move messages to a specific folder. You can move up to 1,000 messages at a time.