In order to set subject line to the beginning of the quoted email, some
improvements need to be made:

Currently the matched "body" part includes the original quote line
("on 01.07.2019, Axel wrote"). Also, try to handle excessive white-space / Line
breaks gracefully in order to avoid overfilling the subject line.

Created an attachment (id=8641) [details]
2.1 pre 249

With this version, you can use the following variable to insert the first 75
characters of the replied email into the subject line:

%header.set.matchFromBody(subject,"(\s*\S){1,78}",0)%

if desired, the subject line can then be extended with ellipses:
%header.append(subject,"...")%

(multiple) newlines and tabs will be collapsed and converted into spaces.

Complete: Release 2.1 - 28/07/2019