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My Zimbra servers daily report always show postmaster as the top sender. There is no postmaster user and greping /var/log/zimbra.log for postmaster returns zero results.
Where is this user coming from and why is it always the top sender?
That's the user that's sending you all those reports. . . May also be sending a lot of bounces to people/spammers that are trying to hit you with bad email addresses, etc.
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Daily Report 
May also be sending a lot of bounces to people/spammers that are trying to hit you with bad email addresses, etc.
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