554 5.3.4 Content conversion limit(s) exceeded

1. Check the size and content of the email: Make sure the size of the email does not exceed the Exchange server's limit (usually 10MB or 25MB).
Check whether the email content contains a large number of attachments or complex formatting (HTML, embedded images, etc.).
2. Adjust the email content: Reduce the size or number of email attachments.
Simplify the email format and avoid using complex HTML or embedded content.
3. Check Exchange server settings: Open the Exchange Administration Console (EAC) and navigate to “Mail Flow” > “Incoming Connectors”.
Check the settings of the Incoming Connector to ensure that there are no overly strict content conversion restrictions set.
4. Use PowerShell to adjust restrictions: Open the Exchange Management Shell (EMS) and run the following command to adjust the content conversion restrictions:
powershell
Set-ReceiveConnector -Identity “YourConnectorName” -MaxMessageSize 50MB -MaxRecipientsPerMessage 500
Replace YourConnectorName with the name of your receiving connector, and MaxMessageSize and MaxRecipientsPerMessage with the desired values.
5. Check Transport Rules: Open the Exchange Administration Console (EAC) and navigate to “Mail Flow” > “Rules”.
Check if there are any transport rules restricting email content conversion and adjust or remove the rules if necessary.
6. Contact Microsoft Support: If none of the above methods work, it is recommended to contact Microsoft support team and provide detailed error messages and logs for further assistance.