getTransportInfo email attachment invalid MIME

V : IS 4.6, platform : Win 2000.
We are facing problem with the email attachment when trying to read from the email box using POP3.
Customer says that the email is generated from the lotus notes application and when tried with the getTransportInfo and savepipeline the contentType and content are coming as blank.Extention of the attachement is .txt.

But when tried to send the same email to the mailbox again using someother email id, the service works very fine.When checked this time the content type is coming as text/plain and attachment can be read for further processing.
Please let me know how to handle such instances or how to actually grab the content type of the customer who is sending the message.!