Each subscriber is assigned a bounce score, as a floating
point number. Whenever Mailman receives a bounce from a list
member, that member's score is incremented. Hard bounces (fatal
errors) increase the score by 1, while soft bounces (temporary
errors) increase the score by 0.5. Only one bounce per day
counts against a member's score, so even if 10 bounces are
received for a member on the same day, their score will increase
by just 1.
This variable describes the upper limit for a member's bounce
score, above which they are automatically disabled, but not
removed from the mailing list.