Message-Id: <lkjsdf01u@example.org>
Date: Sat, 14 Sep 2019 19:00:13 +0200
From: lmn <x@tux.org>
To: abc <abc@bcd.com>
Content-Type: text/plain; charset=utf-8; format=flowed

This line ends with a space 
and will be merged with the next one due to format=flowed.

This line does not end with a space
and will be wrapped as usual.