The current release 2.1.12 needs to be updated to at leas 2.1.18 because unfortunately it is no longer compatible with Yahoo email addresses due to Yahoo implementing DMARC filtering. Because of DMARC when Yahoo email is sent to a Mailman list Yahoo rejects to because mailman modifies headers.
This is something that is clearly Yahoo's fault for bad programming - however ...
Mailman 2.1.18 has new features than cam munge from addresses so that it can fool Yahoo into working. For that reason alone I ask that you upgrade mailman. I tried the Mailman from Fedora 20 and managed to make it work.
there is already bug for this request. I'm closing this as duplicate of Bug 1095359.
*** This bug has been marked as a duplicate of bug 1095359 ***