POP3 re-downloading mail

[Michael Nguyen]

> Sascha Wuestemann wrote:
>
> >On Sun, Nov 07, 2004 at 11:53:52PM -0500 or thereabouts, Warrick
FitzGerald wrote:

Hi Warrick and Sascha,

> >Hi Warrick,
> >
> >seen information is saved at server side for imap and pop3, too.

[snip]

> Let's say you have two POP3 clients one set to leave mail on the server
> for a week and one set to leave mail on the server for a day.
>
> If the one that's leaving thing on the server for a week pick's up mail,
> the other is not effected in any way .. and you're messages are not
> marked as seen in any way. Are you sure POP3 has seen state on the server?

Yes it is...in a way.  It's actually "saved" on both.  Technically it's only
saved on the client, but it uses to the server to tell what's been
downloaded.  The client asks the server to give a "UID" of the messages on
the server.  The client then downloads the messages and records what UIDs it
has seen.  When the client checks mail again, it requests UIDs again.  Any
UID that it hasn't seen, it requests retrieval.

Here's how you can try it out yourself:

 - Open a command prompt
 - Open a telnet session to your mail server on port 110
     - e.g. telnet mail.sascha.fi 110
 - You'll get a POP3 banner.  Login as follows:
    - user <username> <enter>  (this is how your client passes login name)
    - pass <password> <enter> (this is how your client passes your password)
    - list <enter> (this is how your client gets a list of your messages.
You are returned a message number with a message size.)
    - uidl <enter> (this is how your client gets a list of UIDs for each
message.  You are returned a message number with UID)
 - At this point you can get a message using RETR (e.g. RETR 1 will retrieve
message 1)
 - If your client is set to delete messages after retrieval, the client then
deletes using DELE (e.g. DELE 1 will delete message 1)

[snip]

Anyway, what this all means is that the new server-side software merely
recalculated all of your users' UIDs, thus making them appear to be new to
your clients.  POP3 is very simple compared to IMAP.  There is no "seen"
flag.


Michael

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