There was a wide spread attack on AVG and other antispam systems where the network address of their servers was blacklisted. In general you don’t send through Antispam, only receive however many customers choose to send because the recipient is then automatically whitelisted.
This attack caused those customers a series of bounce backs from the more popular mass email domains like gmail, Hotmail, live etc.
Once detected we switched outbound mail to run through the Andisa relay servers and the problem was instantly overcome.
