I tried to build the claws installer for windows and used the HEAD/INSTALL file for build instructions. Debian 10 was the build-system. Running download.sh script causing some error messages because the URL ftp://ftp.cyrusimap.org does not exist.
Same as in the other bug. I am not able to build because of it. So "critical" is minimum.
The FTP address is still listed here, https://www.cyrusimap.org/imap/download/getcyrus.html#build-and-install-yourself It is failing, though. Maybe this is temporary, maybe not. I've changed it to the https address instead.
Please do not use the tracker to request help building Claws Mail for Windows, and please, do not multiply the bug reports for every sub-topic, that's more counter-productive (this will irritate me at least). Check my comments on the other related bugs, and either wait or follow my advices.