There are limitations to sending email itself when using HME. You need to be using an iCloud Mail account only (i.e. email with @icloud.com). This is like saying if you want to be using HME, abandon your current mail provider and come into the Apple ecosystem.

Even after doing that, if you try to add another recipient, it complains that HME can be used only with 1 recipient. I tested this out on icloud.com/mail

Another case is lets say if we don't have forwarding email set to an @icloud.com email, which is the normal usecase everybody probably uses this feature. Their primary email address is either Gmail or Hotmail or whatever. In this, if i set another recipient, the mail contents will probably reach another@domain.com but I am not sure if it will reach sales@business.com because the iCloud MAILER would probably complain the same 1 recipient thing and cause email failure.

Just look at all this complexity & for what? I assume you asked this like a hack to get it working. Even if the email worked, now I have to convince business.com that I am the same user that you have registered as hme-1@icloud.com. What business out there is going to entertain such kind of thing?