This is a support forum for Thunderbird, not mail merge. That add-on lists it's support options on the add-on.mozilla.org web site as an email address.

Thanks for the note. The response to Matt's link: "Sorry, the page you were looking for does not exist or is not available. We performed a web search for “Addon Mozilla” and here's what we found." I didn't find a link on that list which addresses my question. If anyone has a more specific link to try, please let me know.

Mail Merge is a specific extension for Thunderbird downloaded from Mozilla. I had posted a question on this Support Forum earlier today about Mail Merge. The response led to a successful outcome.

I would appreciate any information on the Thunderbird Support Forum to address my original question about Mail Merge posted at 7:34 pm tonight. Thank you.

I did not give you a link, I gave you the name of the website. I also deliberately called is add-ons.mozilla.org. That web site does not exist as a link, it is the name of the site. The forum thinks it looks good and makes it into one that does not work.

The add-on you downloaded came from this URL https://addons.mozilla.org/en-US/thunderbird/addon/mail-merge/?src=search

Down the right side of the screen is a support email. I suggest you use it.

I had posted a question on this Support Forum earlier today about Mail Merge. The response led to a successful outcome.

I beg to differ, you asked how to install an add-on you had downloaded. Personally I would not have answered that question. I would have given you a link to the support article https://support.mozilla.org/en-US/kb/installing-addon-thunderbird but either way you received no support for the add-on. I did however mark airmails answer as a solution so he gets the credit for giving the correct answer.

I have read all the tutorial information of the add-on site and I see no reference to " "Format" field after " Delivery Mode"."

The instructions on the web page say

8. Click "File -> Mail Merge" 9. Select "Address Book" and check "Deliver Mode" 10. Add (individual) Attachments (optional) (variables are supported) 11. Check "Start", "Stop" and "Pause" (optional)

I see nothing like what you are talking about, I have no references to the source of these tutorials you are viewing.

I have looked at https://www.youtube.com/watch?v=l8aOcsojVEo https://www.youtube.com/watch?v=tAkp_GQoX3U https://www.youtube.com/watch?v=juuG_hDR1vQ https://www.youtube.com/watch?v=t5BFoYcx3Nk

I can't see a reference to " Delivery Mode" in any of them.

Deliver mode. Is that the dialog field you are referencing? Am I am obtuse? It clearly does not have a Format box following it. I have had the add-on installed for a fair while now, but I do not recall there being a format on the panel in previous versions either.

Found a youtube like you describe https://www.youtube.com/watch?v=prV2_hAM8X0

But it is clearly not an option in the current version and not a reason for you failure to send. The format of emails is controlled from Thunderbird compose options, not an add-on.