Office 365 - Outlook 2007 Support
This document provides the reasoning behind why Outlook 2007 is not 'officially' supported/recommended in use with Office 365.
The documentation and support team for Office 365 performed full testing of many different clients and versions in use with Office 365. The end result of the testing can be found in the Technical Client Comparison Grid. Testing was performed on those listed in the technical client comparison grid, as well as previous versions of the same clients. You can find the results of our Outlook 2007 testing in the Office 365 (Outlook 2007) - Client Capabilities document.
The overall result of our testing was that Outlook 2007 was able to perform a vast majority of features and functions, and it kept relative pace with Outlook 2010 and 2013 for overall functionality.
So why cancel official support for a working product?
Outlook 2007 works fairly well for the time being; however, Microsoft has a "2 version" support policy. What this means is that they only support a program's current version and one prior version (2016/2013, and best effort support for older versions). Recently Office 365 was upgraded from 'Wave 14' to 'Wave 15' (or in other words, version 14 to version 15), and Microsoft had no intentions of offering support for Outlook 2007 in Wave 15. Due to public outcry and demand, Outlook 2007 was added to the list of supported client versions for Wave 15. Future upgrades to Office 365 may not include support for Office 2007.
We created the Office 365 - Technical Client Comparison grid following the assumption that Microsoft would stick to it's historic policies and end support for Outlook 2007 by the time 'Wave 15' arrived. It seems that Outlook 2007 is still 'supported', but the level of support is already changing and will soon end.
Microsoft's current support for 2007
As of mid-May, 2013, Outlook 2007 is past it's expected end of general support. Going forward, we do not expect Outlook 2007 to be a supported client by Microsoft in future versions of Office 365. Already, Microsoft's product life-cycle policies indicate that support for Outlook 2007 is now in its 'extended' phase, meaning it will include security patches but won't include any "bug" fixes or address any feature requests.
Outlook 2007 will be covered under DoIT's 'best effort' support, but because of this looming end to official product support, we do not list it as officially supported, or even recommended for use with Office 365. This isn't to say the program will not work, because as of right now it seems to work fairly well; we just can't make guarantees it will continue to work as well as it does now further down the road.