Since migrating to roundup2 incoming mail messages generally were rendered with additional line breaks, i.e. each line break was doubled. This was with default setting leave_body_unchanged = no.

Using setting leave_body_unchanged = yes doesn't show this behaviour.

I think it is due to line 1919 in mailgw.py, with

        content = '\n\n'.join(l)

I don't know if there was a specific reason to add two line breaks or if it was by accident, please have a look at the patch attached.