After 1st November 2021 the oldest supported version of Outlook that will be able to connect to Nexus365 services is Outlook 2013 – as long as it has updates and fixes on top. The number of the oldest supported version is 15.0.4971.1000 (Service Pack 1 with the October 2017 Update).
Microsoft are blocking older versions because of the following reasons:
- Support for basic authentication is ending, as a way to improve the security of your mailbox’s content.
- Microsoft are moving towards HTTP/2 – which uses full-duplex communications to decrease latency. Improved header compression and multiplexing help improve throughput even further.
- Newer versions of Outlook crash less often: Outlook’s reporting means that many of the most frequent causes of crashes have been identified and fixed.