#  Create a New Message ("File -> New -> Message")

  #  Create a New Message ("File -> New -> Message")

Perhaps ask the mail merge author on the support link on the download page. https://addons.thunderbird.net/en-us/thunderbird/addon/mail-merge/ Where these instructions are shown 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) # Add (global) Attachments (optional) # Click "File -> Mail Merge" # Select "CSV" as "Source" and check "Deliver Mode" # Add (individual) Attachments (optional) (variables are supported) # Select the "File" and check "Character Set", "Field Delimiter" and "Text Delimiter" # Check "Start", "Stop" and "Pause" (optional) # Click "OK" and Step by Step: (Spreadsheet) # 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) # Add (global) Attachments (optional) # Click "File -> Mail Merge" # Select "Spreadsheet" as "Source" and check "Deliver Mode" # Add (individual) Attachments (optional) (variables are supported) # Select the "File" and check "Sheet Name" # Check "Start", "Stop" and "Pause" (optional) # Click "OK"