Connection Murder Frontend - Backend dropped/instable

[rpr-listen at gmx.de]

Hello

Between my RedHat EL4.0 frontend and backend server i've strange connection problems. I use Outlook and Squirrelmail as mail clients, but so far as I can see, occurs the connection problem between frontend proxyd and backend imapd. Cyrus Imapd V 2.2.12 Patchlevel 8.1

I've created mailbox directorys under /var/lib/imap/log and found
following lines in the logs for the same task:
(Just clicked on each folder)

Backend (one interface to private network:

>1189688791>* STATUS Drafts (UNSEEN 0)^M
zn34 OK Completed^M
<1189688791<py86 Status {11+}^M
Junk E-mail (UNSEEN)^M
>1189688791>* STATUS "Junk E-mail" (UNSEEN 0)^M
py86 OK Completed^M
<1189688791<532b Status {10+}^M
Sent Items (UNSEEN)^M
>1189688791>* STATUS "Sent Items" (UNSEEN 0)^M
532b OK Completed^M
>1189688791>* BYE Connection reset by peer

Frontend (two interfaces, one connected to internet (public)):

>1189688862>* STATUS Drafts (UNSEEN 0)^M
zn34 OK Completed^M
<1189688862<py86 STATUS "Junk E-mail" (UNSEEN)^M
>1189688862>* STATUS "Junk E-mail" (UNSEEN 0)^M
py86 OK Completed^M
<1189688862<532b STATUS "Sent Items" (UNSEEN)^M
>1189688862>* STATUS "Sent Items" (UNSEEN 0)^M
532b OK Completed^M
<1189688862<kf54 SELECT "INBOX"^M
>1189688862>* BYE Fatal error: Lost connection to selected backend^M

---

Sometimes I can see this error on the frontend:

<1189688844<6ewd LIST "" "%/%"^M
>1189688844>6ewd OK Completed^M
<1189688844<c6ag IDLE^M
>1189688844>+ go ahead^M
<1189688845<DONE^M
>1189688845>c6ag OK Completed^M
<1189688845<gr54 SELECT "INBOX"^M
>1189688845>gr54 NO Server(s) unavailable to complete operation^M
<1189688845<g893 IDLE^M
>1189688845>+ go ahead^M

---

And sometimes everything works fine for a couple of minute.
Between Frontend and Backend is a 4mb connection, distance 140km.

Any suggestion where i can look for problems?
Anymore information required?
  
Kind Regards
Reinhard Proessler