XMail gives Timeout

Hello,
My Problem is that sometimes XMail gives Timeout
to my 
users when try send a email (SMTP), never when try
get 
email (POP), is like XMail stop listen the port,
but after 1 minute start to work very well.
The server running XMail 1.18 with Suse 8.0 and
filter 
of Peter Lindeman for virus with f-prot 4.4.1. 
I start XMail with this command line: "-Mx 30 -Mr
24 -
MM -Pt 75 -Pl -Ql -Qt 900 -Qi 1 -Qr 10 -QT 180 -Ph
-Sl -
Sr 300 -Qn 100". 
The uptime of the machine is 0.74 and XMail have
170 + -
 Process Started.
i do not known how can i debug the problem, this
is a 
machine of production and have over 1000 users.

Can you help me, to known what´s happening?.
Excuse me for my english.

Thank you