[Mailman-Users] Problems sending to prodigy.net mail server addresses

[Dmitri Maziuk]

On Mon, 4 Feb 2019 21:29:19 -0800
Richard Johnson <raj at mischievous.us> wrote:
 
> What seems strange is that MOST of the time messages go through just
> fine, but ever now-and-then I'll get this failure notice.

Off the top of my head 1) they've a round-robin cluster of MXers in
which some are configured differently, or 2) they've transient DNS
lookup failures.

FWIW I do have 
  smtpd_helo_restrictions = reject_unknown_helo_hostname
  smtpd_sender_restrictions = reject_unknown_sender_domain
on our servers because vast majority of our legitimate senders come
from .edu addersses (or their home ISPs) while b0rk3d DNS is a common
feature of spam.

-- 
Dmitri Maziuk <dmaziuk at bmrb.wisc.edu>