Email auto add in SPAM-ADDRESS.TAB and SPAMMERS.TAB

Hi

I found the strange problem,
users said cannot send any email and I found user email address register 
in spam-address.tab
but I surely no one add it by manual this problem occur two time but 
difference email address.
it same case in spammers.tab, some time found IP Address register in 
spammers.tab

Please help to advise.
It can add automatic by XMail?
OS: CentOS
XMail v.1.27
No SPAM fitter software install

Regards,
Rittikorn L.
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