ODME Test Connection fails to Office 365, "Invalid Mailbox (Unable to retrieve folders): Object reference not set to an instance of an object" (4348197)

When configuring the On Demand Migration for Email (ODME) Portal Connection Settings for Office 365, you may experience the following error when using the Test Connection feature:

Invalid Mailbox (Unable to retrieve folders): Object reference not set to an instance of an object

First, each account created in Office 365 has a default alias of user@tenant.onmicrosoft.com. Additional primary SMTP domains can then be added to Office 365, such as example.com or domain.com. There are various stages that need to be completed to register primary SMTP domains in Office 365. Depending on which stages have been completed, this may change how accounts need to be entered into the ODME Connection Settings.

In order to receive the error above, typically the following conditions would need to be true:

1.) In the ODME Connection Settings, the "Admin User Name" has been entered as "admin@tenant.onmicrosoft.com".

2.) After clicking "Test Connection", the Mailbox address is entered in as "user@example.com", using a primary SMTP domain.

3.) The primary SMTP domain has been registered in Office 365, however, the required CNAME record for "autodiscover" has not yet been created.

There are two workarounds for this situation:

Workaround 1:

Use the "user@tenant.onmicrosoft.com" address when performing the "Test Connection" feature. Additionally, when adding mailboxes to be migrated during Step 2, add the users using their "user@tenant.onmicrosoft.com" address.

Workaround 2:

Instead of telling ODME to use autodiscover, since no autodiscover record is created pointing to Office 365 for the primary SMTP address, uncheck "Use auto-discovery" and enter the following Server Name for Office 365:

https://outlook.office365.com/EWS/Exchange.asmx

The "Server Name" above is valid for all Office 365 tenants.