Don't worry. This is just the logic of timeouts which is innovative but is not as good as it shall be.

Just to explain it in the simple way. Client sends the portion of the data to the server and waits for the response from the server. Zarafa processes them (adds the data into the database) and sends the reply to the client AFTER the processing is finished. And as processing of the data in your case takes significant amount of time, the client drops the connection because timeout logic starts to think that the connection to the server is not active anymore.

The idea was to address these "faked" connection which happen from time to time especially in mobile connectivity (GPRS etc). But it looks like it does not work as expected with the servers other than MS Exchange (It looks like, MS stuff starts to respond immediately regardless of amount of data the client sends to them).

So, we are now re-thinking the whole idea.