>Hi,
>
>Some of you may have seen my thread about a major memory leak with Outlook 365. I am considering downgrading to Outlook 2010. But, first I wanted to try it. Do you know, if I install Outlook 2010 on the same computer where Outlook 365 reside, if they can co-exist?

Historically it wasn't possible to have 2 different versions of Outlook running side-by-side. The so-called "click to run" installation of Office 365 apparently relaxes that somewhat - with problems: https://support.microsoft.com/en-us/kb/2782408 . However, if you've already done a full install of Outlook on your local machine I don't think you can successfully install Outlook 2010 side-by-side.