> I am in interested in the ways that ALL SMTP servers such as sendmail,
> smail etc and all smtp servers on non-unix platforms handle incoming
> requests on port 25.
> Some require "helo", some "helo ip.ip.ip.ip" some do not require helo.
> Some require vrfy etc.
> I want to know how EVERY single server copes with it and I would much
> appreciate help from the Internet community.
Since most of this behavior is controlled through configuration files,
knowing how EVERY single server handles these situations would mean you
would literally have to know how *EVERY* server (box) (on the entire
network) that happens to be running an SMTP server, behaves. I am not
sure exactly how many servers this encompasses, but I assume it is quite
a large number. Even so, most sysadmins are unwilling to give out such
information for obvious security reasons. If you are writing your own
SMTP, and you want to know what the standards are, check out RFC 821.
In that case, the important thing is that your SMTP adhere to RFC 821.