You are using Office 365 for your email and routing outbound mail through the Symantec Cloud Email Security services, but Out of Office notifications or other automatic replies fail.
The problem is that these types of mails are using a blank (null) sender and the system can only accept outbound relays from Office 365 if the sending domain of the Mail From address of the email in is provisioned on a customer’s account.
You must create a separate outbound connector (which would use Criteria Based Routing scope) to allow auto replies to be routed directly using DNS MX records (instead of routing them through the Symantec.cloud smarthost). A transport rule will need to be created next, which looks for Message type - Automatic Reply and action set to redirect to outbound connector which was created earlier that sends mail direct via DNS. Microsoft's Exchange Online support should be able provide further assitance on configuring your Office 365 service to work in this manner; however, we have determined that the steps below should resolve this issue and route automatc replies through DNS.
Create a new outbound connector to route mail via DNS MX record using Criteria Based Routing scope
1. In the Exchange Admin center, select mail flow > connectors
2. In Outbound Connectors click on + and add a new connector with an appropriate name and description
3. Under delivery, select deliver outbound mail using MX record associated with the recipient domain
4 When defining a Scope, select Use for Criteria Based Routing (CBR) and Click Save.
Transport rule creation
1. Select mail flow > rules, then click on the + to add a new transport rule
2. Name the rule and specify the following conditions:
Apply this rule if... The Message type Automatic Reply with action set to redirect to outbound connector which was created earlier that sends mail direct via DNS MX records
Please note due to Microsoft's changes to the platform the above windows may not be exactly as shown.