This morning I received the following message:

"Your subscription has been disabled on the amsat-bb@amsat.org mailing list because it has received a number of bounces indicating that there may be a problem delivering messages to"

After some investigation I found that the IPv6 address of the amsat mail server is blacklisted by spamhaus, there mail from this address is rejected.

https://www.spamhaus.org/css/removal/record/2600:3c02::f03c:92ff:fe92:3fc7

To the mail administrators please investigate and send a request to spamhaus for list removal.

Jan PE0SAT