Recently messages sent from the Phys-L server were being bounced back from
certain network domains. This means that users whose mail is received at
those domains did not receive these messages.
The reason those domains -- some of them are big ones like gmail.com --
started to bounce messages from Phys-L is due to the IP address of the
Phys-L server being listed in a Policy Block List compiled by a particular
anti-spam organization. The policy that triggered entry to this list is the
dynamically-assigned IP address of the Phys-L server and nothing insidious
like sending actual spam.
I have made changes to the method that outgoing messages are sent to
members on the Phys-L mail list and believe messages will now be sent
without bouncing back to the server. I will continue to monitor the mail
logs and hope this issue is corrected now.