What happens when a message is deemed to be abusive in any way, whether virus, spam, or phishing?

Viruses are treated as any other abusive message. As such they are subject to the prevailing domain or user policy at the time the message was received. These policies include rejecting the message, quarantining the message, or flagging the message.

Is the message rejected, is the sender and or recipient informed and how?

Senders are notified, in the event the message is rejected or quarantined, at the discretion of the originating MTA, via an NDR message. The sender will not be notified in the event the message is flagged. We may introduce an option in the future to suppress sender notification in the event a message is quarantined.

Recipients are notified, in the event a message is quarantined, via a periodic quarantine digest email. The quarantine digest contains a summary of messages that were quarantined since the last digest was issued, and contains links to release the message from the quarantine, block the sender and whitelist the sender. The recipient will not be notified if the message was rejected or flagged.