I'm using Mailwasher Pro to check 4 email accounts. One of them is my partner's business email account. My Outlook is set up to download copies of his emails and his Outlook is setup to download copies of mine. That way, if either of us is out on a service call, the customer's email can be acted upon by the other. Currently, Mailwasher Pro continues to show the email on the POP server, even though my copy has been downloaded in Outlook. My suggestion is to add a column that allows you check a box that says something like "Hide this email in the future", or "Hide this email for XX days" where "XX" would be a user entered variable.

Why don't you just turn on the hide seen e-mail function in MW?

Thank you Stan_Qaz!

For other people that reached a deadend on this subject, the Help files do not have any entries for "hide" which is the operative word in the instructions. Here's how you "hide" emails that you have "read".
Click "Tools" then "Options" and then select the "Display" Tab. Then uncheck the box that is titled "Display read emails". I haven't been successful in finding an explaination of what makes an email qualify as "read". I guess you can experiment and make a determination. Nonetheless, when I followed the instructions above, they disappeared and I was pleased to see that there was a note at the bottom of the email list noting that "4 emails hidden from list"

Thanks again Stan_qaz!

Thanks for the step by step, I can't provide that for the Windows version since I switched to the Linux one.