>my email address is dfroonj@optonline.net.
>
>if I change it to dfroonj@opton, save it, and send a message to it,
>the message never gets delivered but it tells me it got sent.

But it WAS sent. Like a message in a bottle. It went out.

You can send real email like that, manually, to any imaginary address - there's no way any email client can know whether an email is valid or not. It could be brand new, just created a second ago; it may belong to a dead person, be hosted on a server which just vanished in a fire, be hosted by a company which just went out of business, it may belong to a domain in a country which just switched its domain extension from .xx to .xy last night... no way all the email clients in the world would know all that.