I tried some hours getting iMessage to work, after updating to 10.13.5. After many testing, i found that CLOVER was to blame. Before i updated to 10.13.5, i installed CLOVER 4498 (coming from 4428).   Any CLOVER Version i tried prevented activating iMessage (iMessage Error in systemlog: 13)   I tried 4497, 4509, 4458 and 4522. Rolling back to CLOVER 4428 brought back the capability to activate iMessage. iMessage is set up correctly regarding ROM and MLB and never was a issue before.   /EFI/CLOVER/DRIVERS64UEFI has: AppleImageCodec-64.efi DataHubDxe-64.efi FirmwareVolume-64.efi PartitionDxe-64.efi AppleKeyAggregator-64.efi EmuVariableUefi-64.efi HFSPlus-64.efi SMCHelper-64.efi AppleUITheme-64.efi FSInject-64.efi OsxAptioFix2Drv-64.efi apfs.efi   Any ideas why it fails with CLOVER Versions greater 4428?