Please note that on Oct 31, 2017, RPC over HTTP (also known as Outlook Anywhere) will be deprecated in Exchange Online in favor of MAPI over HTTP, a modern protocol that was launched in May 2014. This change affects you if you're running Outlook 2007 because it won't work with MAPI over HTTP. To continue email connectivity, Outlook 2007 customers will have to update to a newer version of Outlook or use Outlook on the web. This change may also affect you if you're running Outlook 2016, Outlook 2013, and Outlook 2010 as you must make sure that the latest cumulative update for the version of Office that you have is installed. For more information refer the related support kb.