[Mailman-Users] the mailman group was deleted on our 2.120 running on ubuntu 18.04. no mail being distributed now

it seems that 1 of our sysadmins inadvertently deleted the group 'mailman'. since then, no mail is being distributed. we re-created the group, but that has not fixed the problem. in order to restore normal operation, perhaps something must be done to this group besides simply creating it. any suggestions appreciated. tnx ams