An "Invalid address" error appears in the log.
Many spam emails contain syntactically invalid email addresses in the from field. Since most SMTP servers (including Exchange Server) refuse messages with invalid from addresses SmartPOP2Exchange gives a warning when it detects such an invalid address.
With SmartPOP2Exchange V7.2 detected invalid sender addresses are automatically replaced with "email@example.com".
For older versions you may create a global rule like this: Condition: "Messages with an invalid sender address" --> Action: "Replace sender address with 'firstname.lastname@example.org'".