POP use of UIDL command ?

It's not clear to me from my RFCs: 1939, 1725, 2449 how the[list unique IDs of mails still on the server] UIDL is used.

I'm speculating that when a list of mails is left on the server and the
client, then the ability to check/synchronize the 2 lists-of-mails is
needed. Provision must be made for the possibility of mail[s] being
deleted from either the server or client, without the corresponding
client or server deletion; which would cause a loss of synchronism.

Q - what would the alrogithm be for using such UIDL facility ?

Perhaps:
ForEach ServerMail: Get the unique-ID;
Compare with the Client's listing & provide info. re. any miss-match.

Perhaps any mails which are on one only of the server and client,
would be marked as such ?

Forcing a synchronisation would need deleting the unmatched
mails ?

Thanks for any info.

== Chris Glur.

(E-Mail Removed) writes:

> It's not clear to me from my RFCs: 1939, 1725, 2449 how the
>[list unique IDs of mails still on the server] UIDL is used.

It's for mail clients that cache message's contents. A mail client that
sees a UIDL for the first time recognizes that it's a new message, and will
download it. A mail client that already saw the same UIDL will not need to
download its contents again, because it already has it.

Recording each message's UIDL is still useful even if the mail client always
deletes messages, after downloading them from a POP3 maildrop. If there's
an exception that interrupted the download process, messages that were
downloaded will still remain on the server (pay careful attention to how
DELE and QUIT works); and the next time the client reconnects it will
otherwise end up downloading duplicate copies of some of the messages.

Recording each message UIDLs will prevent that, since the mail client will
easily recognize message that it already has, making the POP3 mail download
process essentially bulletproof.



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