[Alpine-info] alpine 2.00 and Exchange 2007
mrc+uw at panda.com
Wed Jun 3 13:19:29 PDT 2009
On Wed, 3 Jun 2009, John Hodrien wrote:
> Set-ImapSettings -EnableExactRFC822Size:$true
This was supposed to have been made the default (and only) setting years
> Otherwise, patching alpine to ignore the size is a reasonable response.
> Alpine only checks to see that you got at least as much as the server
> said you would rather than checking for the exact amount, and since
> there's no checksumming etc, you're already winging it as far as being
> sure it's saved correctly.
IMAP is stream-based, not segment based; TCP and the lower levels take
care of reliable transmission and flow control. The only validation check
that is needed is that of size.
The problem is that Exchange lies about the size. This is a big problem,
since Alpine can split the fetch into multiple smaller requests. Alpine
can detect if Exchange sent a long count, but not a short count (it'll
never try to fetch more bytes than Exchange said were there).
So, you had better set "Prevent Partial Fetching" in your configuration as
well. Otherwise you run the risk of losing data!
> There are other problems that *will* bite. Exchange 2007 will return the
> content-encoding as part of the bodystructure response as NIL.
Bug in Exchange and protocol syntax error. From RFC 3501, page 83:
body-fld-enc = (DQUOTE ("7BIT" / "8BIT" / "BINARY" / "BASE64"/
"QUOTED-PRINTABLE") DQUOTE) / string
> seems to interpret this as 7BIT,
Bug in Thunderbird.
> while alpine does not enjoy this, and as a
> result you'll be unable to read some multipart messages. A one line patch to
> alpine fixes this by assuming 7BIT, but it's not ideal.
Basically, it implements the same bug. Your patch is probably relatively
harmless, but there is no guarantee that it won't cause problems in the
> multipart/signed messages result in a broken bodystructure response that
> makes your message unreadable. Save it to a local mailbox and read it
> from there...
Another Exchange bug.
> If you filter on more than about 4 search terms you'll find that you get
> disconnected from Exchange. Exchange returns BAD in response to an
> excessively nested search and disconnects clients who cause too many BAD
> responses (seemingly).
> If you have a near empty mail folder and received new mail, pine doesn't like
> the response. Effectively you get:
> (starting from having one read message in your inbox):
> alpine: NOOP
> exchange: RECENT 5
> exchange: EXISTS 6
Another Exchange bug and protocol error. Messages can not be referenced
in any way until they are defined to exist.
Once again, your patch is probably relatively harmless, but there is no
guarantee that it won't cause problems in the future.
Exchange has a more serious bug in that some versions present EXISTS and
EXPUNGE values out of order. That actually causes real harm because the
client will interpret it in the wrong way. There's no way to patch around
that problem; if you can't get a patch from MS to fix the problem in
Exchange you are screwed.
You've only scratched the surface of Exchange bugs...
Microsoft follows the same strategy with IMAP that it has used with HTML,
Kerberos, and other open-standards protocols: adopt, extend, destroy.
They deliberately mis-implemented IMAP with the specific intent of
breaking (non-MS) clients that use anything but the most basic aspects of
MS has no intention of playing nice with non-MS software, and does so only
when forced by governments under heavy threat of legal sanctions. Even
then, they try to worm out of it.
-- Mark --
Democracy is two wolves and a sheep deciding what to eat for lunch.
Liberty is a well-armed sheep contesting the vote.
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