Hi, one of our clients got this error after sending an email to multiples recepients with a few Yahoo addresses. When we send it individually to the Yahoo addresses they go and when we send a 'mass' mail without the Yahoo addresses it goes.
We have Avast AMS running with the spam filters set to low.
The server has the latest services packs: SP2 for Server 2003 and SP2 for Exchange 2003.
The outgoing server is the local ISP's server smtp.saix.net. We cannot use any other one as they provide connection to everyone and block all other smtp servers.
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