The mail server at 166.82.91.147 uses SpamCop to check and ensure messages are not spam before accepting them. It refused the connection from 216.173.237.164 (SBC mail server) because it has been reported as a producer of spam. All messages from this mail server will not be accepted until the record is removed from SpamCop's database.
This is not an uncommon issue from using hosted email solutions from companies like SBC. Many times the larger mail hosts are not as secure or are abused by other clients and all messages from them get blocked. Some clients like to setup their own outbound mail server to keep this from causing them issues.
It can also be due to the mail server at 166.82.91.147 is not using a updating its SpamCop database and so has stale information to compare its spam records to.