Thank you so much for you suggestions with precise instructions (I need those). The "... so putting it all together you might have:..." was terrific.
The repeated sending to the limited groups of 200 appears to be working great.
I am still concerned about the lack of bounced mail messages. I have the same (valid) email address in the From:, Reply To:, and Return path: fields. I have received some reply's, but not a single bounce message. I know there are some invalid email address in the database.
I also see some blank email addresses in the email log however a small fraction compared to the number of blanks in the database. Any ideas why those exist? I'm confident your suggestion for filtering the blanks is working (for the most part) because many blank rows are ignored. Our MySQL database was created by using SQLyog to import an Excel spreadsheet.