Problem in webmethods/email

Hi All,

I’ve made a port to monitor my mailbox for some purpose.
It’s been proceed well after today i got a message " Error processing email message. null." in my logs.
This mail is not proceed while another proceed well.

everyday i got 5 emails, with the same sender and body.
they are pure direct mail, not replied or forwarded email.
But i do not know why one of them is skipped and return an error above.

could you help me please, what happen in my email port ?

Thanks in advance.