An update for the y!groups mailer list March 8, 2007:

added 209.131.38.0/24

current complete list as of Dec 5, 2006:

69.147.64.0/24
69.147.65.0/24
66.94.237.0/24
66.218.66.0/24
66.218.67.0/24
209.73.160.0/24
209.73.164.0/24
209.131.38.0/24


Adding these addresses to your whitelist helps ensure that client
email is not blocked due to false positives from filters.

For more information about how to read these address ranges,
see ftp://ftp.rfc-editor.org/in-notes/rfc4632.txt

In short, an address block like 209.131.38.0/24 means
all the addresses from 209.131.38.0 through 209.131.38.255
should be allowed to send mail as these are Yahoo! Groups
outbound mail servers.