https://addons.mozilla.org/en-US/thunderbird/addon/mail-merge/?src=ss

Try using the add-on.

mahesh534 said

Thunderbird can be made into a good mass mailing software by having the option of allowing a txt file name in the "To" field. The software then picks up each email address in the txt file and sends the email to each email address individually. Most people keep a list of 100 or 200 or so emails to whom they send regular emails as a txt or xls file. This feature will help enable people use Thunderbird as the mass mailer and send emails to email addresses in a txt or xls file Mass mailing softwares usually cost about $ 50 and this feature will save people this money. Regards

The solution provided worked. However a small suggestion Besides .csv , please also include .txt file option since most users keep email addresses as a txt file. A small change, maybe the writer would like to make this change. Would really appreciate it

Actually you are the first person I have ever heard of that keeps email addresses in a text file that is not internally a CSV file. You have to use a comma or something between the email address and the other information you have on the email address like the persons name.

After all a CSV file is a comma separated values text file.

BTW XLS files export to CSV files, not text unless you want to actually loose information and when you choose text you have to force excal not to include commas.