Mass outbound e-mail sent in 1 day

[Enkrypted]

I was pulling a usage report for the month and noticed an enormous amount of e-mail sent for 1 particular user (like over 5,000). After looking into it, it looks like it was sent on one day. I checked the message tracking for that user on that day and there is no more than 30 e-mails sent from him on that day. I did a usage report for the month prior to that and the same thing exists except for a different user. What could be causing this and how can I resolve it? TIA!

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[Enkrypted]

Anyone have any ideas about this?

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[zbnet]

A virus or some malware on one of your PCs, perhaps?

 

[Enkrypted]

All systems have been scanned/clean so the problem exists elsewhere. I checked and there is no open relay setup, so that wouldn't be a cause.

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