We have ported a number of lists from mailman 2 to mailman 3 earlier. We cannot find any personalization setting in the mailman 3 web UI or using the mailman client. It is fine as it is not essential. However, recently we notice an issue. As the lists in the mailman 2 probably have personalization turned on, it looks like that the setting are also migrated by using "mailman import21". Recently, some users start sending mail simply with Bcc without any addresses in the To header. We notice the following error:

Oct 08 11:26:03 2019 (1832) Uncaught runner exception: 'to' Oct 08 11:26:03 2019 (1832) Traceback (most recent call last): File "/usr/local/lib/python3.6/site-packages/mailman/core/runner.py", line 173, in _one_iteration self._process_one_file(msg, msgdata) File "/usr/local/lib/python3.6/site-packages/mailman/core/runner.py", line 266, in _process_one_file keepqueued = self._dispose(mlist, msg, msgdata) File "/usr/local/lib/python3.6/site-packages/mailman/runners/outgoing.py", line 93, in _dispose self._func(mlist, msg, msgdata) File "/usr/local/lib/python3.6/site-packages/mailman/mta/deliver.py", line 86, in deliver refused = agent.deliver(mlist, msg, msgdata) File "/usr/local/lib/python3.6/site-packages/mailman/mta/base.py", line 163, in deliver callback(mlist, message_copy, msgdata_copy) File "/usr/local/lib/python3.6/site-packages/mailman/mta/personalized.py", line 58, in personalize_to msg.replace_header('To', formataddr((name, recipient))) File "/usr/lib64/python3.6/email/message.py", line 558, in replace_header raise KeyError(_name) KeyError: 'to'

After tracing the source codes above, we suspect that the issue was caused by no To header due to personalization is turned on.

Any quick suggestion of workarounds such as how to turn off personalization for all lists? We do not have much experiences with mailman shell. Thanks a lot.