There are a lot of difference and changes in IMSVA 8.5 and 9.0. When using IMSVA in a complex environment, such as a parent-child deployment, involving both IMSVA 8.5 and 9.0, some features may not work properly and could result in some emails getting lost or mishandled.
After upgrading all instances of IMSVA 8.5 to 9.0, users are instructed to run the dry_run.sh script under /mnt/backup first to make sure that all of the components of IMSVA are upgraded successfully and all features are working correctly.
After running dry_run.sh and confirming that IMSVA was upgraded successfully, finish running the script to verify that IMSVA is working as expected after the upgrade. When everything is working correctly, all IMSVA services should also start automatically.