Hello there :),
aim of the project:
Using the esp8266 to read out calendar data of my outlook account.
Does anyone have experience in reading out outlook mail data by using a microcontroller?
I tried to get access to the microsoft graph, but it doesnt work!
I tried to get access to the microsoft graph
How is none of your business!
I'm not going to tell you what "it" is!
I'm not going to tell you what I mean by "work".
Maybe a few more clues, next time?
Suggest you try to make it work on your PC using a scripting language first to figure out the URLs and OAuth first before attempting to port to ESP8266. The ESP8266 may not have sufficient resources to reliably handle the https:// encryption that's needed.