How to delete left over headers of e-mails which are downloaded?

[Desperate header deleter]

Once I downloaded the ehadres of e-mails and after that downloaded the
message. The headers still stay in the inbox without the possibility to get
deleted.

Does anybody know how to delete the headers from there?

Simply trying to delete the headers by using the delete key does not work.
It tries to delete the message from the server but the server reports back
the non-existence of that message.

Thanks for your help!