help with postfix and roundcube

i have installed postfix and roundcube on ubuntu 20.04 running with postgresql and apache2

i have a very simple demand i need set up a email adress where i will receive daily about 20
emails with xml attachment. a java programm will read it and put content from xml to a postgresql database.

i am java developer and i have a running system like this
my problem is i did not set up the postfix and roundcube a freelancer that is not available any more did

now i need install everything on a new server
i installed postfix and roundcube

postfix can receive emails
but its different than my installation

i have
home/user/Maildir/new
my java programm checks for new mails in this folder all 5 minutes
it will parse xml put data to database and move file from to
home/user/Maildir/cur

in my new installation there is no folder Maildir/new and cur instead it seems all emails are saved
to var/spool/mail/user

all in 1 file

i need the other configuration

also i need help secure postfix so it will not be abused
i need only receive mails and send with roundcobe no client connections

my roundcube installer already works but shows message
in php extensions

dom not -ok
xml not -ok


i need instructions. i dont want to give any server access. i need to learn everything.