Install the EmailAddressCrawler add-on, scan the folder where your filtered messages are placed (right-click the folder, 'Crawl folder for email addresses', or right-click selected messages, 'Crawl selected emails for addresses'), then select "Send using CC (or BCC) field". If there are more than 60 or so recipients, it's probably better to save the addresses to an address book and send a message to a mailing list derived from that address book.

when sending mail BCC using that plugin: mssg: "AN error occurred while sending mail. The mail server responded: <""> invalid address. Please try again.

I had highlighted all filtered messages and right click> selected crawl with....

The add-on works here for a folder or a selection of messages, so I can only guess that one or more of the senders' addresses in your case is causing problems, perhaps there are spaces in the address.

Try selecting the messages 2,3,4.... at a time until you receive the error to find out which address is the culprit.

I did that. I even deleted half of them, and still the same message.

I found a solution. Updated my Thunderbird, and the app worked. I was using v.11 .