This option will initially mark all subscribers that need to receive the campaign as “todo” in the table and then start processing on all the “todo” entries.
It may save a little on SQL time when you have a large amount of subscribers, as the query to search for subscribers is run fewer times.
When MESSAGEQUEUE_PREPARE is 0, each batch of messages is processed as
When MESSAGEQUEUE_PREPARE is 1, the first batch of messages is processed
Then for all subsequent batches:
See also MAX_SENDPROCESSES