Thunderbird mail merge bug or feature?

Is there anyone who knows how to transfer the 0 in an excel sheet (that is a zero) to an email (mailmerge field)? Right now it writes nothing when it is zero in the excel file. If it is another digit it happily transfers it. I cannot decide if this is a bug or a feature.

Just a guess, but I would say the 0 is lost because of the way excel handles numbers Vs text. Try exporting the file from Excel as a CSV file. Open the CSV file in notepad and see if the Zero values show in the file. I would guess not.