Some times messages is deleted from outllok using pop3

[talluricho]

Hi,
we are using outlook client (pop3) for viewing mails.we observed this issue when we click on send & receive in the outlook. We are able to see the mail in the web before clicking on the send and receive option. Once the option is clicked, the mail is getting deleted in the web and not importing into the outlook. we selected leave a copy option in outlook also.It is happening occasionally.When we checked into the mailbox.logs, it is displaying the following message. "mailop - Deleting Message (id=11257)

Can any one help me regarding this? Please, its urgent as important mails are getting deleted.

Regads,
Satyanarayana.