Proxy problem: "[COMPRESSIONACTIVE] TLS compression already enabled"

[Ralf Hildebrandt]

We're proxying using 2.2.14~rc1 (on our IMAP Proxy) to two dovecot
backend servers running dovecot-2.2.13-r1

When we're using Thundebird to connect to the dovecot proxy, we're
getting the message "The mail server for account ACCOUNTNAME
responded: [COMPRESSIONACTIVE] TLS compression already enabled"

But why?

Capabilities reported by the proxy:

. OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE
IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS
THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT
CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC
ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE
BINARY MOVE SEARCH=FUZZY COMPRESS=DEFLATE QUOTA] Logged in


Capabilities of the backend servers when connecting directly:

. OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE
IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS
THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT
CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC
ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE
BINARY MOVE SEARCH=FUZZY COMPRESS=DEFLATE QUOTA] Logged in

-- 
[*] sys4 AG

http://sys4.de, +49 (89) 30 90 46 64
Franziskanerstraße 15, 81669 München

Sitz der Gesellschaft: München, Amtsgericht München: HRB 199263
Vorstand: Patrick Ben Koetter, Marc Schiffbauer
Aufsichtsratsvorsitzender: Florian Kirstein