Jan 18, 2019, 4:08:09 PM1/18/19
When new members sign up for this mailinglist, they are required to
answer a "security" question. It will be very obvious to anyone who is
serious about complex answer retrieval. If a student/coworker of yours
is signing up and gets rejects, s/he probably has not given an answer.
Ask them to sign up again, but answer the question this time.