A viable alternative is Guix, which uses Scheme for its scripts and could also use the Hurd kernel instead of Linux, but works the same.

Oh no, two of the worst companies have left, all we have left now are (…) Google, apple, Microsoft, Uber

So, all that’s left is even worse? ;-)

OpenSMTPD is the default OpenBSD “sendmail”

Not quite. OpenSMTPD is OpenBSD’s default smtpd though (and it is portable!).

Rspamd - basic spam filter

It can be configured to be rather complicated if you wish. :-)

Or XFS.