I noticed Grammarly just entered the AI summarization space for email. https://www.grammarly.com/recap. I haven't tested it yet, but saw the Gmail banner last week.
I found that in my current job I don't so much need a summarization service, but a translation service; what does the writer actually want me to know and to do? I got an email the other day with a lot of brain farts, grainy screenshots, and I had to read it five times just to boil it down to "change this tracked URL to that one".