I need to send bulk mesages Thunderbird will not.

There is a mailmerge utility, mailmerge, that allows this. HOWEVER, sending bulk mail exposes you to being targeted as a spammer. Thunderbird can do the mechanics, but you're still vulnerable. I STRONGLY encourage you to investigate a professional mailing company, such as Mailchimp (or others). The service is free for low volume sending, and, by their doing it, you're safe from being blacklisted for spamming. I could not be more serious. Sending 100 messages makes you a target as a spammer. It may take an hour or so to set up the account, but the benefits are big. For one, you will get reports on which persons actually read the message. :) Good luck.