Evolution understands the kind of meeting request Outlook users mail round. This is good. What Evolution does with them – specifically, how it presents them – needs work.
You're presented with a scrollable area within a scrollable area. The outer scrollable area is the mail itself. It contains the header, and the inner scrollable area. For some reason, the inner scrollable area doesn't fit in the outer scrollable area. Presumably this depends on the size of your screen, but the fact that it's possible at all is stupid. The inner scrollable area serves no purpose and its content should be in the outer scrollable area.
It gets worse. The only thing you need to interact with is hidden away in the most nested part. So first you need to scroll the outer area to the bottom. If you don't, you'll only have to come back and do it, increasing the overall amount of work you have to do. So do that first. Then you can scroll the inner area to its bottom. And then, finally, you can accept or decline.
The components you interact with take almost no vertical space; about as much as one line of text. Why aren't they near the top? Why isn't it easier to see how this meeting request fits on your calendar? What made the authors think they should write such a system without having paid proper attention to existing products? How come this didn't get fixed right away, just after the first time they tried to use it?
It's hard to imagine how they could have done a worse job of this. It actively discourages people from including meaningful information about the meeting in the mail, because that just makes the only bit you interact with all the more inaccessible.