That still doesn't really give you a status of whether the e-mail was successfully delivered or not... that would only help if the domain name part of the e-mail address were valid.or invalid.
As you point out, only the (final!!) destination e-mail server will know whether the e-mail you're sending was successfully delivered into the recipient's e-mail inbox. There are many reasons why the e-mail might not be delivered... including:
1) the recipient's name part of their e-mail address is invalid, or the account has been closed.
2) the recipient's e-mail inbox might be full.
Also, note that there might be MULTIPLE e-mail servers involved... the e-mail address you're sending to might be forwarded to some other address (on the same, or a different server) one or more times before it actually ends up in the e-mail inbox from which your recipient's e-mail client actually reads it from. Any of those servers in the chain could have the issues mentioned above.
Complicating things further, the e-mail you're sending could have multiple destination e-mail adddresses... multiple To: or Cc: or Bcc: addresses. These could all have different delivery statuses.
It's fair to say that you wouldn't WANT blat to delay until all these delivery steps are completed before it returned a status... if it did, it would take a LONG time to complete a large group mailing.
I'll also point out that some ill-designed mail delivery services (like "Constant Contact" IIRC) provide a report to the sender regarding which e-mails have actually been opened and viewed, which they generally do by putting in something like a single-pixel (or bigger!) image embedded in the post, and then reporting to the sender if and when that image was retrieved. Of course, anybody who isn't stupid about such things uses an e-mail client (like Thunderbird) which can be configured to NOT automatically retrieve such remote images when the e-mail is opened...!! Some senders don't understand this, and eventually send me e-mails asking why I'm not opening or reading the things they've sent me. :-((((