We ran into an issue with a particular configuration once that required us to set SmarterMail "MailService" to "Delayed Start" in the Services console - this held off SM's startup about an extra minute or so, while waiting for other "automatic" services to fully start.
Not sure if this will help, but based on the note that iSCSI NAS was not ready, it might make all the difference in regards to the NAS being ready and available first.
I also believe there is a place in the registry to configure the shutdown delay to give SmarterMail service more time and a better chance to cleanly shutdown if that's not happening, but you noted that it was a possible power failure so that wouldn't apply. The default time that Windows gives a service to shutdown is 5 seconds before a process is killed during shutdown sequence, and we all know that SmarterMail can take up to 30 seconds or more to shutdown cleanly.
MailEnable survivor / convert --