Eu tentei os seguintes comandos, mas nenhum funcionou.
/usr/lib/cyrus-imapd/ipurge -d 0 -f "user.admin.*"
/usr/lib/cyrus-imapd/ipurge -d 0 -f "user/admin/*"
/usr/lib/cyrus-imapd/ipurge -d 0 -f "user/admin"
/usr/lib/cyrus-imapd/ipurge -d 0 -f "user.admin"