MTA Level IP Blocking
MTA level IP blocking rejects messages originating from IP addresses blacklisted by SophosLabs. Enabling this option can improve performance by blocking spam before it reaches more complex tests in the policy, such as sender reputation tests.
For installations using PureMessage Sendmail or PureMessage Postfix, configuration of MTA level IP blocking can be done automatically using the PureMessage Manager. Use of other sendmail and Postfix distributions is not supported.