What would cause a (503 5.0.0 Need MAIL before RCPT) error on an
outbound email?

The error is coming up when a user sends to a user along with other
users on the same email. If this user sends ane email to the same user
alone, the email goes through fine.

GW2012sp2 gwia on sles11sp2/oes11sp1 box, 64bit, virtual.