How do you 'mark as read' using Pop3?

Question

I am using an open source client to programmatically process incoming emails (on Windows 2003). The only way to prevent receiving previously read emails is to delete them from the server. This is less than ideal. As far as I know, there is no command in Pop3 to set emails as being read. So how do you go about this?

Answer 1

if you do not want to delete, you have to keep track of all the emails already downloaded and do not RETR them again. afaik there is no "mark as read"-like functionality within the standard POP3 protocol (at least not in the rfc)

Answer 2

It's the responsibility of the POP3 client to check for this. The most reliable method is to use the UIDL POP3 command to get a unique message ID, and keep track of these on the client side.