Step by Step: (CSV)
- Create a New Message (“File → New → Message”)
 - Add the Variable(s) to To, e.g.:
{{Email}} or {{FirstName}} {{LastName}} <{{Email}}> - Add other Recipients to Cc (optional) (variables are supported)
 - Add other Recipients to Bcc (optional) (variables are supported)
 - Add the Subject (variables are supported)
 - Add the Body (variables are supported)
Kedves {{name}}! bla bla {{param}} neduddki - Add the Attachments (optional)
 - Click “File → Mail Merge”
 - Select “CSV” and check “Deliver Mode”
 - Add (individual) Attachments (optional) (variables are supported)
 - Select “Filename” and check “Character Set”, “Field Delimiter” and “Text Delimiter”
 - Check “Start”, “Stop” and “Pause” (optional)
 - Click “OK”
 
Ha magyar a win, akkor nem UTF8, hanem win1252!!!!!!!!!!!!!!!!!!
Windows 1252
https://addons.thunderbird.net/hu/thunderbird/addon/mail-merge/