This post is also available in my podcast.
As per Microsoft, starting on October 13, 2020, only these versions of Office will be supported for connecting to Office 365 (and Microsoft 365) services:
- Microsoft 365 Apps for enterprise (previously named Office 365 ProPlus)
- Microsoft 365 Apps for business (previously named Office 365 Business)
- Office 2019, such as Office Professional Plus 2019
- Office 2016, such as Office Standard 2016
Microsoft states that they won’t take any active measures to block other versions of the Office client, such as Office 2013, from connecting to Office 365 services, but these older clients may encounter performance or reliability issues over time.
The MAPI over HTTP protocol replaces the legacy RPC over HTTP protocol (aka Outlook Anywhere). A very good technical overview of MAPI over HTTP is available in the following Microsoft article: https://techcommunity.microsoft.com/t5/exchange-team-blog/outlook-connectivity-with-mapi-over-http/ba-p/586590. The MAPI Exchange protocol is analyzed in more details here: https://docs.microsoft.com/en-us/exchange/clients/mapi-over-http/mapi-over-http?view=exchserver-2019. Unfortunately RPC over HTTP is no longer supported by Microsoft 365 (Exchange Online) as it reached end of support in October 31, 2017. Since then, there have been updates to Office 365 system requirements.
I recently run into a case where a customer had legacy Office 2007 clients and needed to connect to Microsoft 365 Exchange Online service via these clients. The only viable workaround is to make use of Anonymous Authentication. This can be accomplished by installing Office 2007 SP3 as well as the following patch KB2768023. In case Office 2007 SP3 or the patch cannot be installed then the installation of the .exe should be run from an elevated command line with following parameter: PACKAGE.BYPASS.DETECTION.CHECK=1.
Anonymous authentication in Outlook also resolved the issue with persistent authentication prompts when connecting to Microsoft 365, as per the following article: https://docs.microsoft.com/en-us/outlook/troubleshoot/sign-in/continually-prompts-password-office-365
If you are still working on Office 2010, 2013 or 2016, you need to ensure that you have the latest updates installed for running smoothly with Microsoft 365 Cloud services. Details on the required service packs and hotfixes for each legacy version of Microsoft Office are available at: https://docs.microsoft.com/en-us/officeupdates/outlook-updates-msi
Further details about Office client compatibility with Microsoft 365 can be found at: https://docs.microsoft.com/en-us/deployoffice/endofsupport/office-365-services-connectivity