To set up live mail archiving from your O365 to Vaultastic, the first step is to define an SMTP Connector to route mail from O365 to Vaultastic. One common mistake is to give your Vaultastic domain URL instead of o365.vaultastic.com as the Smart Host.
To correct, make sure the email domain in the step to deliver mail "Only when email messages are sent to these domains" is your Vaultastic domain and the Smart Host is "o365.vaultastic.com"