Hey kbekus,
you should check the output of the following command
grommunio-admin user query username maildir
and compare it with
ls -d /var/lib/gromox/user/*/*/
I assume there will be five folders and you might guess it by now that the one which isn't listed in the first command should be the old maildir of that user.
I would "backup" both folders of the user just to be sure nothing goes missing
tar cfvz oldfld1.tgz /var/lib/gromox/user/X/Y
as well as the other folder
And after that you could shutdown the gromox-services(because i don't remember right now which exactly, but you have a small system so no bother)
systemctl stop gromox-* nginx
move the new maildir away and move the old one in its place and after that start the services.
# For instance the old user was in /var/lib/gromox/user/0/2 and the new one is in ../1/1
mv /var/lib/gromox/user/1/1{,.bak}
mv /var/lib/gromox/user/0/2 /var/lib/gromox/user/1/1
systemctl start gromox-* nginx
And if everything seems ok you can remove the backup of the new maildir
I think i covered everything... 🙈
Good Luck!