If another clients wants to download a file from you, he will request this file and reask every 10-20 min to make sure that you are still a valid source. However it is possible to adjust clients so they ask more frequently. This will give the modified client a higher chance to get an upload slot on eDonkey clients.
eMule does not care about the reask frequency and the chances to get an uploadslot won't increase. Such behavior wastes valuable resources (connections and bandwidth) and will be blocked.
The new client system will blacklist clients which reask too often (more than once for a file within 10 min), and they are not allowed to download from you. The blacklist is cleared when you restart emule.

Examples how to get blacklisted (you won't be able to download from emule clients):

> Setting the reask-parameter of your client lower than 10 min.
> Setting your downloads to pause and resume to increase your downloadspeed regulary - which will result in a new filerequest everytime (eDonkey clients only)
> Restarting your client every 2 min (which will also result in a new request).

To make it clear: eMule does not care which client (eMule/eDonkey/mldonkey/shareaza) asks. Each client that reasks too often will be banned.