This error (Response status code does not indicate success: 422 (Unprocessable Entity)) is caused by saving an attached file (file of the converted email in .msg format).

This error can be caused by the fact that you are trying to save a file that is not an allowed format in your Redmine.

Please check (or ask your Redmine-administrator for this) that allowed extensions contains the format of the email which does you save in the task.

You can do it by going to Administration -> Settings -> Files -> Allowed Extensions.

Also, this field can be empty. In this case, you can add files of any formats to the task.

If into Allowed Extensions does not have the format you need, please add it. This should solve the problem you are facing

Also, notice that you can add email files in other formats (such as .txt, .html, .rtf) or completely disable attachments to attachments. You could do it by going to Redmine Ribbon -> Settings -> Convert tab.