We have decided to upgrade to Office 365 and have already migrated from Exch. 2003 to Exch.2010 to be able to migrate easier to Office 365 Exchange Online. AD FS 2.0 is installed on ISA Server (Srv 2008 R2 Std)

Public DNS records are modified as explained in portal.office.com
There are 5 certificates (3 self signed, 2 third party) assigned on Client Access Exchange Server but still not able to create a migration endpoint over portal.coffice.com.

We are always getting an error related to certificate and still it is not clear what to do more or next.
When I check with the connectivity analyzer I get this error message:
"The Microsoft Connectivity Analyzer wasn't able to obtain the remote SSL certificate. The certificate couldn't be validated because SSL negotiation wasn't successful. This could have occurred as a result of a network error or because of a problem with the certificate installation."

I already sent the analyze report to Microsoft support but they answered with some article links.

Where exactly these certificates should be assigned on? Any suggestions?

Hi Louis,

Did you get any error when you tried to create a migration?

I recommend you refer to the following article to migrate the mailbox data:

How to migrate mailbox data by using the Exchange Admin Center in Office 365

This article describes the migration features that are available in the Exchange Admin Center in Microsoft Office 365. It also discusses migration scenarios in which the Exchange Admin Center is used to migrate data from the following existing environments:

• Microsoft Exchange Server 2003
• Microsoft Exchange Server 2007
• Microsoft Exchange Server 2010
• Microsoft Exchange Server 2013 
• Internet Message Access Protocol (IMAP)

About certificate error, base on my search, I found a similar thread with the same issue as yours, however, it due to office 365 not use SSL certificate to verify the account, you can ignore it safely. 

http://community.office365.com/en-us/f/148/t/171279.aspx

In addition, I also recommned you post this in Office 365 forum .

Best regards,