Post History
It's totally fine. It expresses a combination of query and astonishment. There was even an attempt to combine the marks into one, called an interrobang, but it never caught on. Using "?!" is neithe...
Answer
#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/48376 License name: CC BY-SA 4.0 License URL: https://creativecommons.org/licenses/by-sa/4.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/48376 License name: CC BY-SA 4.0 License URL: https://creativecommons.org/licenses/by-sa/4.0/