Set up a summary field (I'll call it "emailList")pointing to the email address and a calculation field that has a calc like the following:
Substitute ( emailList ; "¶" ; ",")
Then use that as your BCC when sending out the email.
Note: I don't know what the maximum limit on this will be with both FileMaker or your mail server.
"everyone" may label you as a spammer by many email applications. I like to break these into smaller chunks of 25 or less per email.
What Bev said and putting a 30 to 60 second timer between each chuck will help as well
After re-reading the original post, my reply did not address your question... sorry... "never mind"