Hi Group,
I have configured MSILO with following modparams.

modparam("msilo", "db_url",DBURL)
modparam("msilo", "offline_message","$rU is offline!")
modparam("msilo", "extra_hdrs", "Msilo-msg: true\r\n")
modparam("msilo", "outbound_proxy", MSILO_OUTBOUND_PROXY)
modparam("msilo", "content_type_hdr","Content-Type: message/cpim\r\n")
modparam("msilo", "extra_hdrs", "Content-Type: message/cpim\r\n")
modparam("msilo", "add_date", 0)

MSILO dumps all the messages to destination immediately after recipient registers and gets 200 ok for sent messages. 
The delivered messages are not cleared immediately and takes a minute to delete each message.

Could some one explain why the delay is observed?

In case you need to know I am using Kamailio 4.0.0 on CentOS 6.5

Thanks & Regards,
Prasun