Resolution
This error indicates that one or more phrases in the incoming mailing were identified as part of an error, command or out-of-office message by ListManager.
To fix this, navigate to:
- Utilities: Administration: Server: Server Settings: Automatic Maintenance: Error Mail
- Set "Disable Subject: checking:" to Yes.
More information about this setting can be found by clicking the Help (?) icon in ListManager when viewing the Error Mail page.