Hi Mathias,

thanks for the report and the suggested fix.
I checked out one of our roundup emails and it had the doubled headers.
So I consider the problem confirmed.

However before removing the lines like you have done in your patch,
I think I must find out why they are there in the first place?
There must be a situation where they where necessary, maybe with an 
elder email python module or a different change elsewhere.

Best,
Bernhard