Rated 5 out of 5 stars

le Calliope ar DFómh. 9, 2015 · buan-nasc

A very clever and reliable extension I use every few months or so. It works perfectly for me and it's usually the first add-on I install on new machines with Thunderbird on them.

As another user pointed out, the ms-dos comma separated format works best.

And there are dozens of variables you can use in your multi-recipient mails which is very useful.