How to stop all downloads before certain date

There are 80,000 messages to me stored on I cannot afford to erase or loose any of them. I want them to stay there forever. But I want eMclient to download to my computer eMclient area copies of all new messages that appear on from this point onward. But no older messages.

How do I tell eMclient to do that?
Thank you.

In other words I want my eMclient Inbox to have only a few messages, just the new ones. And the online client ( to keep all 80,000 old messages there.

It does not seem to be possible but maybe this article from the knowledge base helps: