On Sat, Oct 27, 2012 at 11:05 PM, David Abrahams <[email protected]> wrote:
>
> I just set up my Gnus to put a copy of every message I send into my
> local "All Mail" box. GMail already puts a copy in my remote "All Mail"
> box. Then I ran mbsync, and didn't see the message twice in my local
> "All Mail." Did I get lucky, or does mbsync have a way to avoid
> generating duplicates of a message when it appears, via other means, in
> both local and remote mailboxes? Is this in fact just one more
> testament to mbsync's total awesomeness?
I've did a similar "experiment" and my guess is: GMail detects
duplicate emails and stores them only once; `mbsync` is oblivious of
this issue.
Now about my experiment: I have a very old archive of my emails
(from other accounts than GMail) that I wanted to "import" into GMail,
but I wasn't sure if some of those emails weren't already in GMail
(because at some point I've used some forwarding schemes). Thus I've
done the following:
* created a new label in GMail, and exported it through IMAP;
* made `mbsync` "push only" to that label;
* copied the file from the "all-mail" maildir (and changed it's name);
* ran `mbsync` to push the email;
How did I verify:
* searched through GMail search interface to see if that mail was
duplicated (it had a "unique" subject);
* made `mbsync` pull the "all-mail" maildir and checked if the
file got duplicated;
The result: it didn't got duplicated neither in my maildir, nor in GMail.
What didn't I try, that could possibly duplicate it:
* alter the headers related to routing;
* alter the `Message-Id` header;
* alter the subject and body;
I'd verify those because I don't know how GMail detects
duplicates. It might:
* use a hash of the entire email (envelope with headers + body);
(thus any change in any of the above would make it double the email);
* maybe it uses only `Message-Id` header to detect duplicates;
(thus any change in any of the above would make GMail just pick one
version;) but I doubt it is this;
* use a combination of headers, body, etc. to detect duplicates;
(for example it could ignore the routing headers;)
Hope this helps,
Ciprian.
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