Exchange 2003 SP2 staged migration to O365

Copper Contributor

Hi Friends,

We are running single exchange server (Exchange server 2003 SP2) and looking for staged migration to O365. I have enabled RPC over HTTP proxy and added the certificate and the certificate is trusted by the server. But outlook connectivity tester always fails to connect my exchange and because of this iam not able to migrate. When iam accessing the OWA through HTTPS it gives error connection closed (but it works well on IE). In all browsers OWA through HTTP is working fine.

Outlook connectivity tester gives error - Testing the SSL certificate to make sure it's valid. The SSL certificate failed one or more certificate validation checks

Please help to solve this issue

1 Reply

Please check.
1. Your certificate must be created from Unified Communications certificate partners.
Unified Communications certificate partners
2. Please test the connection from
3. Please check your step
Perform a staged migration of email in Exchange Online

4. Please check Basic Auth on your tenant.

UPDATE: Exchange Online deprecating Basic Authentication (Basic Auth)


Example On-Premises Exchange 2003 to Microsoft 365 Migration Guide