spamassassin blocked valid mail

[dhanushka ranasinghe <pa...@gmail.com>]

Hi...

My spamassassin threshold value is configured as 4.8 , and anything above
this value will be mark with "X-Spam-Flag: YES" by exim.

but recently i saw mail with  X-Spam_score: 2.5 got block and ,mark with
"X-Spam-Flag: YES" flag, is there any reason for that,

following is the message details,

MIME-Version: 1.0
X-Spam_score: 2.5
X-Spam_score_int: 25
X-Spam_bar: ++
X-Spam_report: Spam detection software,
	running on the system "spamassassin.ihk.com", has
	identified this incoming email as possible spam. The original message
	has been attached to this so you can view it (if it isn't spam) or
	label similar future email.  If you have any questions, see
	@@CONTACT_ADDRESS@@ for details.

[...] Content analysis details:   (2.5 points, 4.8 required)
	pts rule name              description
	---- ----------------------
	--------------------------------------------------
	3.6 FS_REPLICA             Subject says "replica"
	-1.9 BAYES_00               BODY: Bayes spam probability is 0 to 1%
	[score: 0.0000]
	0.8 RDNS_NONE Delivered to internal network by a host with no rDNS
X-Spam-Flag: YES
X-Mailman-Approved-At: Sun, 22 Jul 2012 19:57:07 -0700



Thank you