The graph DB is used for storing folder structures. It doesn't contain actual emails. When the graph DB is deleted, MailArchiva should resync the folders in Exchange / Azure.
Database Service Not Started
Error message is: The database service is not started
Option 1) Delete Database
Windows
Stop MailArchiva service
Delete C:ProgramDataMailArchivaROOTdatabase
Start MailArchiva service
Linux
/etc/opt/mailarchiva/stop
rm -rf /var/opt/mailarchiva/ROOT/database (delete the database)
/etc/opt/mailarchiva/start
MailArchiva will create a new database.