According to Apple discussion boards, Mail can handle a group of 100 names or more. I created one that has 27 names, but Mail keeps telling me that it can't send the message using my designated server (ameritech). Howver, it could send OTHER messages using that server just fine. Just to check, I took out 2 names, bringing the group down to 25, and it sent the exact same message. Put the two names back in -- nothing.
As I said, when I investigated on the apple boards, someone else had the problem -- but supposedly Mail will let you put 100 names in the list before it gets too long. A mere 27 is a long way from 100...
Anyone else run across this issue? I usually use entourage, but I wanted to use Mail for this, creating a smart mailbox that I could keep synced between machines.