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Chris, many thanks. &nbsp;That helps
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I have a simple one domain, one exchange server (2003) system. &nbsp;One of my 70 users came in the other day to find 500 undeliverable messages in her Outlook. &nbsp;They were all spam using her account.I checked MXLOOKUP and we do not have an open relay. &nbsp;There are only a few messages in my System Manager queue. &nbsp;This is a one-time occurrence. &nbsp;Should I ignore it and see if it repeats? &nbsp;Or what should I check to prevent a reoccurrence. &nbsp;Our incoming mail goes through a spam filter, but I don't believe our outgoing mail does.
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I have a simple one domain, one exchange server (2003) system.  One of my 70 users came in the other day to find 500 undeliverable messages in her Outlook.  They were all spam using her account.I checked MXLOOKUP and we do not have an open relay.  There are only a few messages in my System Manager queue.  This is a one-time occurrence.  Should I ignore it and see if it repeats?  Or what should I check to prevent a reoccurrence.  Our incoming mail goes through a spam filter, but I don't believe our outgoing mail does.

Somebody sent spam using one of my users accounts

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.