[Users] [Bug 3049] New: Claws fetches all messages instead of only new & doesn't rely on imapcache

[noreply at thewildbeast.co.uk]

http://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=3049

            Bug ID: 3049
           Summary: Claws fetches all messages instead of only new &
                    doesn't rely on imapcache
    Classification: Unclassified
           Product: Claws Mail
           Version: 3.9.3
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P3
         Component: Folders/IMAP
          Assignee: users at lists.claws-mail.org
          Reporter: the.solipsist at gmail.com

## Summary ##
Even though my entire email account has been cached (synchronised offline),
each time I open a folder (via IMAP) in Claws, it goes through the process of
re-downloading all headers and message bodies from the remote server, meaning
it often has to download hundreds of MB before it even shows the message list.

## Background ##
I've recently shifted to using Claws on Ubuntu, having installed it from the
PPA (version 3.9.3).

I connect to my organization's mail through IMAP (say,
imaps://mail.example.org).  To create a local cache of all my email, I did the
following:

1. Created a local user with the same name and password as my organizational
email account
2. Downloaded a copy of all mails using OfflineIMAP, pointed Dovecot at it
3. Modified /etc/hosts to redirect mail.example.org to 127.0.0.1
4. Loaded Claws, configured it to connect to mail.example.org.  I tried opening
the various folders to see the message list.  It took 5 seconds to 3 minutes to
open any folder depending on its size.  (I've folders with anywhere from 10
messages to 21000 messages.)
5. Went to "Properties for folder #imap/[example]/INBOX" and checked
"Synchronise for offline use" and checked "apply to subfolders", with "fetch
message bodies for 0 days".
6. I clicked on File > Synchronize folders, and waited for a couple of hours.
7. I checked ~/.claws-mail/imapcache/mail.example.org/[username] and that is
now 10.4 GB, meaning it has cached all my mails.
8. I tested this by opening Claws and browsing through the folders.  The
message list takes just as long to open as was the case in step 4.
9. I clicked on "Offline mode".  Every folder opens up instantly as does every
message. (I clicked "No" when asked if I wanted to temporarily go online.)

10. With trepidation, I modified /etc/hosts to remove the redirection from
mail.example.org.
11. I opened Claws, and it takes ages to open any folder with more than 10
messages.  It took me around 5 minutes to open a 50 MB folder with around 300
messages.  While this is happening, I can't do anything else, and have to wait.

I went through the various IMAP-related bugs here, but couldn't find one that
was appropriate.  I did however find this, which describes my bug:
https://bugs.launchpad.net/ubuntu/+source/claws-mail/+bug/221503

I've gone through
http://www.claws-mail.org/faq/index.php/General_Information#Why_does_Claws_Mail_load_big_folders_slowly.3F
and ensured that all of the options that slow things down are turned off.

Is the above behaviour usual / expected?  If so, how

Is this the expected behaviour?  Is there an option to change this behaviour? 
If not, how do people use IMAP folders with more than 50 mails, and what
exactly is the purpose of imapcache?

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