[exim] how to delete "frozen" emails permanently

>>    exipick -zi | xargs exim -Mrm

>>
>>exipick is a very very useful tool.
>>
>>
Hi,

I just noticed that some these "frozen" email are coming back to my
email server again. How can I remove them permenantly from Exim email
system? I m using Exim 4.4

Thanks
Sam