Amavis before 2.12.3 and 2.13.x before 2.13.1, in part because of its use of MIME-tools, has an Interpretation Conflict (relative to some mail user agents) when there are multiple boundary parameters in a MIME email message. Consequently, there can be an incorrect check for banned files or malware.
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.