Sieve with plussed delivery / 'seen flag'?

[Karl Pielorz]

Hi,

We're running Cyrus IMAP 2.4.17. We've got sieve rules used for accounts - 
and some users use 'plussed' addresses.

For example, I've setup a Sieve rule that matches on a subject of 'Test':

"
require ["fileinto"];
require ["imapflags"];

if header :contains ["Subject"] ["Test"] {
  addflag "\\Seen";
}
"

This works fine e.g. if we email 'user at example.com' - with a subject of 
'Test' it'll appear in their inbox as 'Seen' mail (i.e. already read).

However, if we do a direct delivery to a subfolder e.g. email 
'user+sent at example.com' - the mail appears in that folder, but appears as 
'Unseen'.

Weirdly, if we change it to do:

  addflag "\\Seen"
  addflag "\\Flagged"

And send an email to the plussed address, it arrives - is Flagged, but has 
not had the 'Seen' flag added to it? (i.e. it arrives as Flagged, Unseen).

Does anyone know why this is? - Or how we can fix it?

'anyone' has p rights to the destination folder (and during testing we gave 
'anyone' all rights to the destination) with the same effect.

Thanks,

-Karl