POPmonitor is $25 shareware. In an unregistered version of POPmonitor you can create one mail account, three trusted senders, three blocked senders and three custom filters.
After registering you can create an unlimited number of each.

Please register if you use POPmonitor on a regular basis or if you want to remove the limitations of the unregistered version.

You can obtain a registration code as follows:
– Go to www.paypal.com
– Select the Send Money option
– Enter the recipient's e-mail address: leo@makkinje.nl
– Enter the amount: 25 USD
– Follow the onscreen instructions to finalize the payment

Once the payment has been processed by PayPal you will receive a registration code per e-mail. In POPmonitor you can click the Enter Code button in the startup screen or select the Register menu option to enter your name and your personal registration code.

Please note that you should not purchase a registration code if you are planning to use Mac OS X 10.7 because POPmonitor will not be compatible with that version of the Mac operating system.