Yeah, in your case, the most I see could be done, is to remove the address that gives an unreachable response and add it to a list which can be referred to, right before a mail to the next record's address is sent (to not retry duplicates).

Or maybe use some AI mumbo-jumbo to determine availability.

Of course, I can also think of using DNS records to precheck if the domain name exists, but I would think they would mostly be parked domains anyway, so maybe not.