Thank you Mark, for your help.
I could see, that there was no data in the tcpdump between postfix and
amavis.
Due to the speed_option, i could see, that postfix doesn't completely
receive the mail from the client,
so there is no problem with amavis, as i expected without the speed_option.
I can see, that the client is on a DSL connection, and delivers very
very slowly,
until it runs in a timeout. It can send only 1.451.523 Bytes in 23 minutes.
I thought of a MTU problem on the client side, but in the TCPdump i saw
traffic from client to server (very slowly).
In the end, the connection was terminated.
So I don't care any more, because this seems to be a client's problem.
Thanks for your help!
Carsten
