Made major progress today. I am down to one small issue, which I believe is definitely an Opt-In Email glitch, but everything else is now resolved.
I am going to post a great deal of detail here, not to resolve my problem, but to help others who may run into the same peculiarities.
Our problem began a few weeks ago when we moved our domain email services away from our hosting service (3Essentials, who are terrific, by the way) to Google Apps. We thought we had made appropriate setting changes to use Google SMTP, but apparently not, and that was a major part of our trouble.
Late last night, we opened a ticket with 3E, and they quickly came back with an offer of a special email account we could use for SMTP sending. It took a little monkeying to get it right, but once that was in place and we could send a message with DNN bulk mail, we were on the way to solving our Opt-in problems. So with DNN SMTP set to use webxx.3essentials.com as the server, and our new account domain@webxx.essentials.com set as the credentialed account, with a successful send test, the rest of our problems began to disappear.
We no longer needed to use alternate configuration, and our default from address of noreply@domain.com worked as it was supposed to, whether via send immediate or schedule immediate.
So our bottom-line lesson was, if we move our domain email to a different service, we need an smtp sender in the hosting provider's network (in our case, the same server as is hosting our site).
I said there was one glitch, and here it is:
Sending to a list of 376 addresses, all but three went fine. The three that didn't gave a message in the send schedule of:
Sending To (0 of 76 - Maximum of 100 can be distributed with this distribution): kenmrobbins@gmail.com
From Email Address: The Harvard General Store
What these three addresses have in common is they were all three associated with accounts that were logged in when the schedule was executing. We thought at first it might be that they were local addresses, that had been moved to Google Apps, but in fact, only one is.
They ended up at the top of the list, but in fact, they originally occurred at differnt parts of the first three groups of 100. Because they failed each time, they were attempted again in the next run of the schedule.
Ideas?