Re: Avoid POP3
On Wed, 18 May 2011 12:28:31 -0400, Miles Fidelman wrote:
> Camaleón wrote:
>
>> On Wed, 18 May 2011 10:32:01 -0400, Miles Fidelman wrote:
>>
>>> The protocol is very specific - listing headers, downloading/reading
>>> messages, marking messages for deletion, and actually deleting
>>> messages (when a QUIT is issued) are very distinct operations that
>>> have to be executed via different protocol transactions. There is no
>>> inherent combined download/fetch/get/retrieve/delete action.
>>>
>>> There may be default actions set up in a client, but those are client
>>> and configuration specific.
>>>
>> Do you *really* think that pop3 is *widely* used to do not get and
>> delete the messages from the server? I don't think so, and moreover, I
>> would not recommend to keep the messages on it because it can cause a
>> big mess on the client side, better use imap.
>>
>>
> I didn't say that - I said that there is no inherent combined operation
> in the protocol - if read/delete are bundled, it is either by action of
> a client invoking the protocol, or by an out-of-band action on the
> server side.
Next time you need to configure a POP3 account tell me if you leave
enable the "keep a copy in the server" setting. It's not the default, it
never has been in any MUA, or not in any I'm aware of. I don't think how
is that so hard to understand.
> And YES, to the extent that pop3 is still used, there are lots of cases
> where people leave messages on their server - for example, checking mail
> from a smartphone, then downloading and saving it later from a computer
> at home or office. (And, perhaps, as pointed out in RFC1918, using the
> pop3 server as a cheap mail repository.)
Yes, it can be used, of course, it's an optional feature that can be
provided by your e-mail server.
(...)
>> P.S. Recommeded lecture:
>>
>> - RFC1939, chapter "8. Scaling and Operational Considerations" -
>> http://en.wikipedia.org/wiki/Post_Office_Protocol#Extensions
>>
>>
> Actually, I have.
>
> RFC1939 gives a somewhat expanded statement of the intent of POP3 (vis
> POP)
>
> "The Post Office Protocol - Version 3 (POP3) is intended to permit a
> workstation to dynamically access a maildrop on a server host in a
> useful fashion. Usually, this means that the POP3 protocol is used to
> allow a workstation to retrieve mail that the server is holding for it.
>
> POP3 is not intended to provide extensive manipulation operations of
> mail on the server; normally, mail is downloaded and then deleted."
>
> Note the word "normally."
Yes, I've noted, I hope you also did :-)
> And then in Section 8, among other things, states:
>
> "In these situations and others, users and vendors of POP3 clients have
> discovered
> that the combination of using the UIDL command and not issuing the DELE
> command
> can provide a weak version of the "maildrop as semi-permanent
> repository" functionality
> normally associated with IMAP."
> And goes on to recommend that commercial operators consider such actions
> as: "Imposing a per-user maildrop storage quota or the like" and/or
> "Enforce a site policy regarding mail retention on the server" and go on
> to note that "Such message deletions are outside the scope of the POP3
> protocol"
>
> The section notes, explicitly that:
>
> "Clients must not assume that a site policy will automate message
> deletions, and should
> continue to explicitly delete messages using the DELE command when
> appropriate."
>
> -----
> Which brings us back to the original question that started this thread:
Well, at last someone re-read the original post!
> "We have a problem. We are building an app which uses Roundcube to read
> mails. It's ok for IMAP accounts, but we need to read an account
> provider who just uses POP3. We need to read it without download the
> mails. There are some way to read the mails from POP3 account without
> download...maybe a gateway to IMAP...some idea?"
>
> Whether IMAP is a "better" solution or not; whether it's a good idea to
> leave mail on a POP server; and whether some clients default to deleting
> messages after downloading them by POP3 are all irrelevant to the
> question.
(...)
They're not irrelevant.
I read it as if the OP is currently *downloading and deleting* the e-
mails that come from the POP3 server... but he can read the messages
without downloading them, many pop3 checkers do that way! And I just said
this, no more, no less.
> What are relevant are:
>
> 1. Clarifying that "read without download" is simply not possible, but
> that read, but leave on the server is.
I already explained this in my very first e-mail on this thread:
http://lists.debian.org/debian-user/2011/05/msg01463.html
> 2. POP3 does NOT inherently delete messages after they are read
It's the default action, but you can use another words if you like.
> 3. There are both clients and software libraries (and probably gateway
> services) that can:
> - pull mail from a POP3 mailbox
> - make that mail available via IMAP
> - AND leave the original mail on the POP3 server
Of course, there are also fetchmail and getmail for that task and you can
instruct both applications to keep a copy in the server.
> 4. There is a risk that the the operator of the POP3 server might
> implement out-of-band mechanisms to delete messages after they are read
> - as a matter of site-specific policy and mechanisms.
Sure there is. There is even the possibility that the pop3 server (or
client) does not provide such "uidl" capability.
> What also might be relevant is clarifying the original poster's intent.
Exactly!
> Why is someone "building an app which uses Roundcube to read mails" -
> given that Roundcube already IS an app to read mails. If the question
> is "how do we extend Roundcube to access POP3 mailboxes?" that leads to
> a very different answer (e.g., a plug-in or gateway) than if the OP is
> writing an application that has email as an internal function - in which
> case, that tends to lead toward use of a package of mail-access library
> routines, rather than an email client like Roundcube.
Just a side note on this.
You are not aware that the OP sent the same question to the Spanish
mailing list and I replied to him in there becasue I first saw the
question in that list... and I asked him to clarify what was his exact
intention, what was he wanting to get because I was not very clear to me,
neither.
> What is definitely not helpful are factually inaccurate statements like:
> "pop3, due to its own nature, inherits by default a
> "download/fetch/get/retrieve and delete" and then attempts to further
> justify such statements with further inaccurate statements and with
> references to binding documentation that states exactly the opposite.
Sir, just two things:
1/ The "inaccurate statements" can be because I'm not a native English
speaker and my English vocabulary is not as good as I would like (or as
it can be yours). I hope you can understand that.
2/ The RFC (and also the Wikipedia article) clearly say that UIDL is not
intended to be used as a "poor" copy of the imap features, that is, to
keep messages on the server and follow their state (seen, read, etc...)
nor to track them.
This is from Wikipedia:
***
"(...) An extension mechanism was proposed in RFC 2449 to accommodate
general extensions as well as announce in an organized manner support for
optional commands, such as TOP and UIDL. The RFC did not intend to
encourage extensions, and reaffirmed that the role of POP3 is to provide
simple support for mainly download-and-delete requirements of mailbox
handling..."
***
And I think the last paragraph is very contundent on what pop3 was
designed for.
Greetings,
--
Camaleón
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