I administrate two Mailman mailing lists at ScienceByEmailHTML and ScienceByEmailPlain. We have approximately 39 000 addresses in the former list, and about 1000 in the latter. I have a question about the bounces we receive.
We have the lists set so after five bounces, the address is automatically disabled. An notification is sent alerting us to the disabled account, where we then delete the address from our own records as well as Mailman.
Depending on the week, we can get over a hundred of these notifications which come in batches, arriving typically on Friday (although we also get waves coming in on Monday as well).
However, we can also go a week without receiving a single one. Given the spread of excessive bounces is often in excess of a hundred, and rarely fewer than 60 or 70, I'm wondering if you know why this might be the case. Also, why do they arrive in waves? Is it collated and sent periodically through Mailman, or is it a result of batches of bounces being sent back from servers?