[MlMt] Moving large IMAP folders

[Benny Kjær Nielsen]

On 11 Jan 2014, at 23:20, Bill Cole wrote:

> The way to do that with a correctly-behaving IMAP server is to create 
> a new folder, copy all of the existing messages into it, and delete 
> them from the original folder. This seems to be what MM does and it is 
> a less risky and more universally workable strategy, but in principle 
> it should be possible to do a real tree rearrangement with one RENAME 
> command instead. I am interested in *why* Benny chose not to use 
> RENAME.

That's a good question. I had completely forgotten this part of the IMAP 
RFC. I cannot recall any other reason for not using it than the current 
behavior means that I can do the same thing no matter what action the 
user has taken (renaming or dragging a mailbox to a different location 
or even a different account — it's all a variation of moving 
messages).

With respect to performance. For MailMate it would not be more efficient 
to use RENAME. It would just be a different code-path. Some servers 
though probably handle RENAME much more efficiently — and for some 
servers it would also mean that quota limits would not come into play.

In any case, the biggest performance problem with renaming IMAP 
mailboxes is not solved by RENAME. It's only the email client doing the 
renaming that can handle it efficiently. All other (offline) email 
clients are, at least in theory, going to clear their caches and then 
refetch all messages in renamed mailboxes.

@Kee: Yes, MailMate should be smarter about renaming (and moving) a 
parent mailbox.

I'll put IMAP RENAME on the list of potential performance improvements.

-- 
Benny
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