I am sure that it can work on a Pi.
However, it looks to me like james is not pure java and so that package includes pre-built binaries. They will be compiled for x86(-64) and will not work on any model of Pi.
You need to start with the "Source code" version from here: https://james.apache.org/download.cgi#Apache_James_Server
There is ...
if you use web interface then the owner of the files will be the user that web server is running with, right?
if you cannot work on this (I am not sure if you can set up umask or so) then you can always put in crontab every minute the command to change the permissions - but I am sure it has to be possible on the apache config