[Mailman-Users] Reject by default - will the spam increase?

[Michael Stucki]

Hi all,

due to a big spam amount, I have switched my lists to only accept mails from
list members.

After to weeks of production use, I note that many people use a wrong email
address (not the one they used for the subscription).

Therefore, I'd like to send a rejection response on all messages from such
non-members.

My question is: Since spammers are non-mebmers as well, will their bots
understand my response as a validation (this address is being read) or will
he handle it as an error response and probably delete it from the list?

What would you do?

Thanks - michael