The mailing list for listmasters using Sympa

["Ascoet Stephane" <address@concealed>]

 Hi, I'm volunteer in an Internet provider and we get spams on our Sympa contact adress(sympa-request@ourdomain). Listmasters receive them, Sympa answers them and often, we get a non-delivery mail in response. So, for each spam, we can have one message sent and two messages received by each listmaster! Since senders of these non-wanted mails are often the same ones, I'd like to blacklist them like I can do for individual mailing lists. Does Sympa permit it? May you have any other idea?