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From "Danny Angus" <da...@thought.co.uk>
Subject RE: James POP3 versus RFC 1939
Date Thu, 26 Apr 2001 15:44:48 GMT
>
> I've successfully authenticated to the same account twice at the same time
> using Outlook, but I just chalked that up to the overall poor quality of
> software from that vender.

Outlook is a client, you can't connect to the same server twice (except
James right?) this is a function of the server.

>
> > if a mail client uses the sequence number of listed messages then a
> > concurrent delete throws the numbers out.
>
> Could you elaborate here?  I must not have had enough coffee yet
> because I'm
> having trouble following this.

POP3 lists messages, and assigns them sequential numbers, these numbers are
only valid for the messages during this session, once you quit and re-list
the same message could have a different number.

This happens if an intervening message in the is deleted by another session
between your sessions.

hence you always need to list before you know what you can get or delete.
If another session connects at the same time they could delete a message,
and quit, then the messages will have different numbers than your ongoing
session thnks they have EG..

session one LISTs and is told about messages:
1 (hello)
2 (foo)
3 (goodbye)

session two connects and is give the same list, BUT the user of session two
deletes 2 (foo) and quits, actioning the delete on the server.

session 1 now tries to retrieve 2 (foo) but gets 2 (goodbye) because the
list (if session 1 asked) is now...
1 (hello)
2 (goodbye)

its simple really.

The problem is that the rfc has stated that maildrops are locked during
connections.
Therefore clients *dont* have to take steps to avoid this trap, which I
suspect might not be possible anyway.


its a vicious circle.

d.



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