https://wiki.koozali.org/User_homes_admin_access can be used to directly access user homes,
then folder by folder copy/move out emails (sorted by date) from Maildir folders and rename files to *.eml.
Don't copy anything to Maildir folders without setting ownership to user:user, otherwise users won't have access to them.
I use this custom-template: /etc/e-smith/templates-custom/etc/smb.conf/55adminhomes
[admin_homes]
comment = home_directories
path = /home/e-smith/files/users/
valid users = admin root
admin users = admin root
write list = admin root
public = no
browsable = no
writable = yes
then:
expand-template /etc/smb.conf
systemctl restart smb
now go to \\serverIP\admin_homes (with the two-panel file manager of your choice)