Microsoft have been informing business customers using older versions of Outlook to upgrade to newer software before the 1st November 2021.
After this date, only Outlook 2013 Service Pack 1 (with the most up-to-date patches) and later versions will be able to connect to Microsoft 365 Exchange.
Why use the newer versions of Outlook?
Microsoft wants to move away from the basic authentication systems used in older versions of Outlook and instead ensure everyone connecting to its Microsoft 365 services use more modern and secure protocols. This will also prevent cyber security problems from external threats so it does make sense.
Plus with it’s 365 business plans (Standard and Premium) that already include the Microsoft suite of apps to download to Macs and Windows PCs, there is no cost to upgrade to newer versions of Outlook.