Microsoft reaffirmed the company's presence at E3 2019 via its official Xbox Twitter handle shortly after Sony confirmed that they are pulling out of E3 for the first time in the show's 24 year history. We aren't sure of Microsoft's plans for the event but expect a lot of information on upcoming consoles and exclusives.
https://www.notebookcheck.net/Microsoft-confirms-E3-2019-participation-after-Sony-pulls-out.362176.0.html