Exchange 2010 calendar publishing URLs are not updated after migrating to Office 365
With Exchange 2010 Service Pack 1 it became possible to share your calendar with anyone outside of you organization, depending on the Sharing Policy implemented by your Exchange Administrator. Users can then share their calendar via an obfuscated or an relatively public URL without the need for authentication (and SSL for that matter). For more information on how to prepare your environment if you want to enable it, see this blog post.
However, if an user has this enabled on an On-Premises Exchange environment and is then migrated to Office 365 the URL pointing to the published calendar is not updated and will probably not work.
I migrated my personal on-premises Exchange account to an Office 365 P1 subscription, after that the URL did not work anymore. This was logical as the original URL did not point to a published Exchange server from Office 365 (which uses *.outlook.com, at least for P1 plans).
Disabling (Stop Publishing) and (re)enabling calendar sharing by the user generated a correct URL and calendar sharing worked perfectly fine after that.