[Mailman-Users] Unsubscriber problem

Hi I have mailman 2.1.8. along with postfix. Everything is fine. now from few days i watching few of my sunscriber from list automatic get unsubscribe, without knowing anyone. Could you tel me the causes ??? On membership list i am finding B option in nomail reason??? whats this???

Re: [Mailman-Users] Unsubscriber problem

python python sent the message below at 04:04 4/6/2007: Hi I have mailman 2.1.8. along with postfix. Everything is fine. now from few days i watching few of my sunscriber from list automatic get unsubscribe, without knowing anyone. Could you tel me the causes ??? On membership list i am finding B