If you send a postcard via land mail, the post office doesn't keep a copy from it if you lose it after you've received it.
Originally Posted by stasouv
From POP3 RFC1939:
POP3 is not intended to provide extensive manipulation operations of
mail on the server; normally, mail is downloaded and then deleted. A
more advanced (and complex) protocol, IMAP4, is discussed in
Like the RFC says solution is to stop using POP3 and use IMAP instead if you want the mail server to protect stupid users from themselves.
Other obvious option is of course to train your staff/clients and stop assuming they'll figure it out.
If you have people configuring client machines for someone else, provide correct configuration instructions to them so they can perform necessary steps.
That seems stupid to you, but if you have a checklist saying "I selected the option to leave copy of messages to server", then the client is configured like you suggested.