"To:" will put all the addressees in the To box and they will all see each other's addresses. Whilst this may be appropriate in some business correspondence, it is, as I am sure you are aware, very bad practice with private email addresses, and in some legislations may be considered criminal. And of course it is inappropriate in commercial "bulk" or "mailshot" situations.

I think you need a Mail Merge facility. This will take a list of addresses, and generate a customized discrete message for each address. Usually it can drop into the body text of the message personal items such as name, mailing address (think of those Readers' Digest letters we used to get in the regular mail) to generate the illusion that the message was written exclusively to the addressee.

Thunderbird has a Mail Merge add-on which can do all this. I don't have any reason to use it myself but in testing I found it rather fragile. It didn't handle faults very well, and if it stopped mid-run, it was hard to know what had and hadn't been sent and therefore avoid repeat mailings when restarting.

The mail merge in your office productivity software might be more effective. The free Libre Office suite has a built in mail merge capability which can operate independently of Thunderbird.

If you're doing this routinely you may well get into quota or spam limitation issue with your email provider or ISP, unless you have a paid-for business grade account with generous traffic allowances. Using a third party such as mail chimp or constant contact may be a better way to go about it.

Zenos,

Thanks and appreciated. I was also thinking of mailchimp. I think that is the way to go forward. Thanks again.