We're having some problems with 44net email to and
from
hotmail.com. Mail from that domain is getting delayed,
sometimes for hours, and mail going to addresses in that
domain is received by the server but not delivered to the
users mailbox.
I sometimes have similar problems with
gmail.com. I send replies to
allocation requests to the user's gmail address and they never receive
it, and become impatient and repeat the request. Sometimes I can fix it
by using a different sender mail address.
It looks like those big guys (who of course get billions of spam messages
a day) use a lot of sender profiling and low-volume senders like @amsat.org and
@*.ampr.org get low in their reputation score. So with a *.ucsd.edu sender
address you had a quite higher reputation score. Mentioning IP addresses in
the mail body does the rest. (often considered an indication of spam)
Rob