have you opened the CSV file in a text editor and looked to see what is there. My guess is Excel is removing them. It did in Excel V2, I so no reason why that would change.

Why start a new thread for the same question if you are not going to read the answer to your original post? This is a function of Excel and has nothing to do with Thunderbird.

Here is your original post and solution. https://support.mozilla.org/en-US/questions/1014147

Moderator Matt, you are right the LDIF and TAB versions had the leading zero. However the horizontal layout of the CSV records is more to my purpose, so how can I recover a CSV file also will the leading zero in place?

More specifically, if Excel is the culprit, can Thunderbird instruct it to fall in line or can the CSV file be delivered to another program - if so how?

In excel reformat the cells as phone numbers (I think I recall such a formatting option, it has been years) I gave up on Microsoft products when that god awful ribbon appeared. I am a happy convert to Libre Office

@Airmail, At the moment as the forum is basically a mess with mails notifying responses taking up to 72 hours to be sent and search is basically useless. I have filed bugs and send nastygrams about it to the relevant Mozilla people. So now we just have to wait it out

did excel formatting work?

In short no - when I open the CSV file in Excel 2007 mysteriously some telephone numbers are without a leading zero. Libre allows telephone numbers to be declared text before the spreadsheet is opened.I haven't tested the import step. I am not able to do that for MS excel 2007.

I conclude the Thunderbird CSV export option does not support MS excel 2007. In future I will use the character O instead of a leading 0.

For me the thread is closed. Thank you all the same Moderator Matt.

For the next person to come along, here are Microsoft instructions for formatting leading Zeros in Excel. http://support.microsoft.com/KB/81518

An image of the phone number being set to text in Excels import Wizard. I don't have the 2007 version available to test, but I do not recall it being any different about a decade ago.