If you are still running Exchange 2010 you are most likely aware that the end-of-life of Exchange 2010 is in January 2020 when extended support will end.
Because of the size of customer still running on Exchange 2010 and the amount of work it takes, especially for large enterprise customers, to move to newer platforms, Microsoft has extended the extended support to October 2010.
After October 2020, Microsoft no longer support Exchange 2010. This means no bugfixes, no security fixes, no hotfixes, nothing. The product won’t stop working of course, but no fixes will be released by Microsoft, and especially no security fixes can be dangerous.
Note. The support for Office 2010 and SharePoint 2010 is also extended to October 2020, so these are aligned now.
If you are still running Exchange 2010, it is recommended to move to Office 365 or to Exchange 2013 or Exchange 2016. Please note that there’s no direct upgrade path to Exchange 2019, so you have to move to Exchange 2013 or Exchange 2016 (preferred) first before moving to Exchange 2019.
A lot of my customers are moving to Office 365, and I have written two blog posts on this. These are based on Exchange 2010 hybrid, without the hassle of installing Exchange 2016 first into the existing Exchange 2010 organization:
I am not sure, but when support for Exchange 2010 stops in October 2020 support for Exchange 2010 hybrid stops as well and I wouldn’t be surprised that Exchange 2010 hybrid will stop working anytime soon after this date.
If you are still running on Exchange 2010, or working on an upgrade to Exchange 2016 or Office 365, you have some more time to finish these projects, but please don’t slow down at the moment and continue your projects.
You can find the official Microsoft announcement here: https://techcommunity.microsoft.com/t5/Exchange-Team-Blog/Microsoft-Extending-End-of-Support-for-Exchange-Server-2010-to/ba-p/753591