The best solution is to submit the mail as a false positive using the instructions here: https://www.symantec.com/docs/HOWTO77719
If there are time constraints, a temporary measure to make sure mail is able to be sent exists.
- In the Control Center, click on the Administration tab.
- Go to Users -> Policy Groups in the left column.
- Check the group you wish to edit, then click the Edit button above.
- Click the Spam tab in the Policy Group settings.
- Remove the checkmark from "Enable outbound spam and unwanted email scanning for this policy group".
- Click the Save button at the bottom.
This process may take some time to make its way through the scanners.