Hello Joseph. 

My view on your point 3. 

The downgrading happens on Server and when email goes out of server it will be just like any other ASCII email, which you could have sent otherwise, hence there is no reason that downgrading will invoke any special case for antispam. 

However there may be rules required for mixscript check, variants, emojis etc, which antispam companies allows the administrator to configure (such as smpamjadoo.com) for support of IDN and how many checks they wish to perform on characters. 

Thanks 

 

Don and all,