Some Permissive SMTP Servers (like AOL) will send an "OK" response to the RCPT command, even if the user doesn't exist. That's called a "false positive".
In order to avoid false positives, you should turn the safemode on:
Go to the Tools | Configuration | Servers and check the "Save Mode" box.
Now, all "false positives" will have the status "Permissive Relay".