[Dovecot] Error in IMAP command UID: Unknown thread algorithm.

[Ralf Hildebrandt]

Our Squirrelmail offers "Thread based sorting".
Now, I have one user, where the activation of thread sorting results in:

FEHLER: Falsche oder ungültige Anfrage.
Anfrage: THREAD ORDEREDSUBJECT ISO-8859-1 ALL
Server antwortete: Error in IMAP command UID: Unknown thread algorithm.

Why is that?

-- 
Ralf Hildebrandt
  Geschäftsbereich IT | Abteilung Netzwerk
  Charité - Universitätsmedizin Berlin
  Campus Benjamin Franklin
  Hindenburgdamm 30 | D-12200 Berlin
  Tel. +49 30 450 570 155 | Fax: +49 30 450 570 962
  Ralf.Hildebrandt at charite.de | http://www.charite.de