dovecot sieve duplicates detection

André Rodier andre at
Mon Apr 23 23:03:21 EEST 2018

On 23/04/18 14:18, Stephan Bosch wrote:
> Op 11-4-2018 om 23:58 schreef André Rodier:
>> Hello,
>> I have tested the sieve duplicate script with success so far, but I have
>> a question.
> Sieve duplicate script? You mean the Sieve duplicate extension (RFC 7352)?
>> I would like to know if the "duplicate" sieve flag in Dovecot is global
>> to all folders, or specific to one folder only.
> It uses the lda-dupes file in the user's home directory. So, it is not 
> normally related to folders, although the identifier used for duplicate 
> matching could be composed of the mailbox name if you want.
>> For instance, if I copy an email from one folder to another, and I have
>> a discard action on duplicate email, is this action will be applied (in
>> this case, discard) or not.
> Are you talking about IMAPSieve now? I am not sure "duplicate" is 
> currently even allowed in that context.
>> If the duplicate is global to all folders, is there a way to restrict
>> the search in one folder only.
> You can set the :uniqueid parameter accordingly.
> Regards,
> Stephan.

Thank you, Stephan.

Yes, I meant the Sieve duplicate extension.

I am using a program to import email (mbsync), which use the IMAP append 
function. Sometimes, the import fail and I have to restart the program. 
Unfortunately, the same emails are imported again.

I found a fix by using a dovecot IMAP sieve script executed on the 
APPEND action 
( I wrote a 
custom sieve script that "discard" the ones that are detected as 
"duplicate". It worked very well and the emails were not any more 
imported twice.

However, there was a huge side effect: archiving an email with 
Thunderbird is not working any more, and even lost! I have been able to 
understand the error as this:

1. When archiving an email with Thunderbird, it is first copied (APPEND) 
into the archive folder, but the original folder is not expunged.
2. The sieve script detect the email as duplicate, and discard it.
3. When the original folder is expunged, the source email is lost...

My conclusion was the duplicate detection function is global to all folders.

If I could restrict the detection of duplicates in the current folder 
only, this would let me run the import program again without error.

Kind regards,

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