POP3 in general
The pop3 protocol doesn't have a server-side tracking which mails have already been retrieved. A mail client typically retrieves a mail and deletes it on the server afterwards. If the client is configured to not delete mails, then the last step is omitted and the client keeps track of which mail it already has.
POP3 server not known to the proxyIf a mail gets caught, the proxy replaces it with a notification right away in the same connection. The quarantined mail can be viewed in mail manager, but is not associated to a server or account and therefor can't be released in a later connection.
POP3 server known to the proxy (prefetch disabled)Same as above, but the proxy keeps track which quarantined mail belongs to which server/account. So it can be released if the client polls the mailbox next time. For this to work, the proxy has to savely identify which ip addresses belong to which server (FQDN which you have entered in your mailclient).
POP3 server known to the proxy (prefetch enabled)The connection between client and server is asynchron. The proxy only presents clean mails to the client, which it has downloaded before. It keeps track of which mails it already have. Clean mails gets only deleted on the server if there has been a delete command from the client before. There will be no notification for each single quarantined mail, instead there is a daily quarantine report.
Thank you for continuing to define clearly how the POP3 proxy functions. Again, restating to make sure I understand...
There is an error in the design of the menus and documentation for the Astaro POP3 Proxy. The proxy is virtually useless unless it knows the 'POP3 Servers' being used by POP3 clients behind the Astaro. The list should be on the 'Global' tab along with an indication that quarantined emails cannot be released for POP3 servers unless they are included in this list.
It's time to make this work.
