Welcome to the forum Jogi13,
Hmm, it works for me. Please reboot your computer and then try the "Hide Read" button again.
If the issue persists after a reboot - then (from the main POP Peeper menu) please go to "File" (upper-right corner) and select "Error overview...". This will open the "Error overview" dialog (it will appear empty) - please click on the "Copy Log" button (click "OK" to the next prompt), close the the Interface, go to this topic in the forum and paste (right-click, select "Paste") the information into your reply in this topic. This will provide us with helpful information (in-part your versions of Windows and POP Peeper as well as additional information).
If you do the above you can skip questions 1 & 2 below (as they would then be redundant)
Just a few questions (assuming the issue persists after a reboot):
1) What version of Windows are you using?
2) What version of POP Peeper are you using?
3) What software do you use for security? (Firewall, Antivirus etc)
4) How long have you been using POP Peeper we need to know:
4a) Whether you just recently installed POP Peeper and this function has never worked or
4b) the "Hide Read" function has worked in the past but now it doesn't?
5) If the answer to #4b above is "Yes" - have you installed any software (i.e. security software) that would align with when this function stopped working? -- If you have what software would that be?
6) Anything else you can think of that could in some way impact POP Peeper?
Thanks.
Addendum: To be clear - "read" messages will display the "open" envelope icon as illustrated in this screen-shot example:

- Click on the image to enlarge for better readability (use the browser back-arrow to return to the topic)
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