When viewing the logs, a large number of warnings of the following content were found:
Invalid sender. "@" is missing. BATV tagging will be skipped
What is this error and how to get rid of it?
Please be informed that the following warning refers to Bounce Attack Prevention technology to eliminate non-deliverable receipt (NDR) messages that are a result of redirection techniques commonly used by spammers.
It can be avoided safely as SMG shows the following when an email does not contain a "Bounce attack signature" to validate the email hence is the reason for the warning.
More details about Bounce Attack Prevention can be found in the Administration guide on page 132.