[Mailman-Users] Suspending Requests for Subscription

[certuspersonality]

Some scammer has discovered the possibility to subscribe to my 
Mailman subscriber list and is now inundating me with requests for 
subscription.

So far, I have dealt with the requests by rejecting them through 
Mailman, but the next day there are new ones with different email addresses.
Is there a way of suspending requests for subscription temporarily?

Regards,
Herward