To configure multiple O365 domains in your organization,

Step 1: Define separate SMTP Connectors to route mail from Office 365 domains to Vaultastic
This step has to be done for each of the O365 domain. The SMTP connector for each domain will have to be configured using the journal id corresponding to the Vaultastic domain, which will receive mail for the O365 domain.
Refer to the steps to configure the SMTP host

Step 2: Define a single recipient for Non-Delivery Reports.
The recipient for Non-Delivery Reports can be from any of the O365 domains. The recipient for NDR can be changed at any time.
Refer to the steps to set NDR recipient

Step 3: Configure separate Journal rules for each O365 domains
Each O365 domain will need a separate journal rule.
Refer to the steps to configure journal rules