[MlMt] Some notes on the new QUOTA feature

[Benny Kjær Nielsen]

Hi,

this is a technical email for the few people interested in some 
low-level details of the QUOTA support in MailMate.

As some of you probably have noticed then the new QUOTA feature has had 
various problems with specific servers. I believe most of those issues 
are fixed now. The last couple of problems were server bugs and I just 
wanted to share them in case someone wonders what MailMate is doing to 
work around them.

The first one results in behavior like this:

~~~
...
S: * LIST (\HasChildren) "." INBOX
S: A5 OK List completed (0.001 + 0.000 secs).
C: A6 GETQUOTAROOT "INBOX"
S: A6 NO Internal quota calculation error (0.001 + 0.000 secs).
~~~

MailMate didn't handle the `NO` response gracefully, but it still 
indicates some kind of server issue (this was Dovecot). I've changed it 
such that MailMate just continues as if QUOTA was not supported.

The second one is worse:

~~~
C: A1 CAPABILITY
S: * CAPABILITY XAPPLEPUSHSERVICE IMAP4 IMAP4rev1 ACL RIGHTS=tekx 
CONDSTORE ENABLE QRESYNC QUOTA NAMESPACE UIDPLUS CHILDREN BINARY 
UNSELECT SORT CATENATE URLAUTH LANGUAGE ESEARCH ESORT 
THREAD=ORDEREDSUBJECT THREAD=REFERENCES CONTEXT=SEARCH CONTEXT=SORT 
WITHIN SASL-IR SEARCHRES METADATA ID XMSEARCH XSENDER X-SUN-SORT 
ANNOTATE-EXPERIMENT-1 X-UNAUTHENTICATE X-SUN-IMAP XUM1 MULTISEARCH IDLE
S: A1 OK !!
C: A4 LIST "" "*"
S: * LIST (\Noinferiors) "/" "INBOX"
S: * LIST () "/" "Archive"
	...
S: A4 OK LIST completed (took 25 ms)
C: A5 GETQUOTAROOT "INBOX"
S: A5 BAD Parse Error
~~~

The server claims to support QUOTA, but then fails with a `BAD` error 
which is the server's way of saying that MailMate did something wrong 
with its command (which is not true). This is an iCloud server, but the 
problem only exists for some iCloud servers. For some reason Apple do 
not use the exact same IMAP server implementation on all of their 
servers. This is also the main reason I'm writing this email. I wanted 
to write down why some users might have QUOTA support for an iCloud 
account and others do not (or maybe even the same user at different 
times).

The workaround in the latest test release of MailMate is to 
“temporarily” disable the QUOTA support whenever receiving the `BAD` 
response as seen above.

-- 
Benny
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