[2.3.1] Sieve daemon : closes connection at once on some conditions (?)

[Vincent Deffontaines]

Greetings,

I am having a quite weird behaviour from the sieve daemon.

I have in my config (SERVICES) :
sieve         cmd="timsieved" listen="sieve" prefork=0

The daemon listens fine on TCP port 2000.

If I telnet to localhost on port 2000, I get :
Trying 127.0.0.1...
Connected to sexa-mail1.ecn.loc.
Escape character is '^]'.
"IMPLEMENTATION" "Cyrus timsieved v2.3.1"
"SASL" "PLAIN"
"SIEVE" "comparator-i;ascii-numeric fileinto reject vacation imapflags
notify envelope relational regex subaddress copy"
"STARTTLS"
OK

Which I am happy with.

If I telnet from another box from the same network (10.0.0.0/8), I get the
same prompt.

If I telnet to it from a host on another network (dmz - 192.168.X) :
Trying 10.1.122.49...
Connected to sexa-mail.ecn.loc.
Escape character is '^]'.
Connection closed by foreign host.

The connection opens, and gets closed straight away.
So this is not a firewall nor a routing problem. I get in the logs on  the
sieve server :
Feb 15 23:20:25 sexa-mail1 master[26216]: about to exec
/usr/cyrus/bin/timsieved
Feb 15 23:20:25 myhost sieve[26216]: executed
Feb 15 23:20:25 myhost sieve[26216]: telling master 2
Feb 15 23:20:25 myhost sieve[26216]: accepted connection
Feb 15 23:20:25 myhost sieve[26216]: telling master 3
Feb 15 23:20:25 myhost master[17464]: service sieve pid 26216 in READY
state: now unavailable and in BUSY state
Feb 15 23:20:25 myhost master[17464]: service sieve now has 0 ready workers
Feb 15 23:20:25 myhost master[17464]: service sieve pid 26216 in BUSY
state: now serving connection
Feb 15 23:20:25 myhost master[17464]: service sieve now has 0 ready workers
Feb 15 23:20:25 myhost master[17464]: process 26216 exited, status 0
Feb 15 23:20:25 myhost master[17464]: service sieve now has 0 ready workers

So the process just closes the connection and exits with status 0.

Is there some config option that I don't know of?
Is there something obvious I am not seeing?
Why is there no prompt when connecting from that host?

Vincent