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

Marc Schiffbauer m at
Wed Oct 15 02:06:49 UTC 2014

* Timo Sirainen schrieb am 15.10.14 um 01:39 Uhr:
>On 14 Oct 2014, at 16:10, Marc Schiffbauer <m at> wrote:
>> * Timo Sirainen schrieb am 15.10.14 um 00:57 Uhr:
>>> On 14 Oct 2014, at 15:24, Ralf Hildebrandt <r at> wrote:
>>>> 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?
>>> Is the connection from proxy to backend using SSL? Did this work in earlier Dovecot version?
>> I talked to Ralf about this issue today. Yes, proxy to backend is using ssl. And yes when proxy is talking to a 2.1.17 backend there is no issue.
>Right .. If the TLS connection already has compression enabled, Dovecot will refuse COMPRESS command. But it should be checking this against the original client's TLS connection and not the proxy's. As a workaround you could set in Dovecot backends "ssl_options = no_compression". I'll try to figure out how this should be fixed properly.

Timo, thanks for the workaround. After finding out that this 
requires 2.2.14 too (had 2.2.13 before) it works like a charme now.


[*] sys4 AG, +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

More information about the dovecot mailing list