Thunderbird uses one line per email address. Hence all those TO fields.

It also allows the user to enter one email address after the other separated by a comma followed by a space. Although I'm not sure if you did this after all it is the slowest, most long winded method with the highest probability of errors.

I tested: Manually type email address, immediately followed by comma then a space then second email address; all sent and received with no issues. But this long winded method is totally unnecessary and prone to an easy mistake.

eg: accidentally putting a space before the @ will produce the double quote error you are seeing.

If you used a semi-colon instead of a comma, then it will also fail because the semi-colon does not separate the email addresses, so they look like they are joined by a space which gives same error.

Mailing Lists are designed to be used when sending one email to a group of people and the group is always the same, although you can add and remove from the group. It does not sound like you are using a Mailing List. Q: Are you using a Mailing List which is a sub group of one of your address books in thunderbird?

Thunderbird Write window is designed to enter one email address per line. Usually, the contact has already been added to your address book, so you would normally use the Contact sidebar to select serveral contacts and then click on eg: 'AddtoTO' button to auto entry all those email addresses one per line in one go. Q: Are you doing it this way - do you use the Contacts Sidebar?

I performed a test: I added a contact to my address book. email address: peter@somwhere.com where there is an inserted space before the name peter, of course this is not instantly noticeable, but it is as if you had hit the space bar just before typing the email address.

Then when I use the Contacts Sidebar in a Write message, it will add the email address like this: Peter Foo <" peter"@somewhere.com> which of course in invalid.

but in the address book, if highlight the contact, in the section below the email address in blue - the highlighted email addess does not include the 'space'. If I click this to send an email the email address is printed correctly and it will send as if nothing is wrong. So, i can produce the error if the email address has been added to the address book, but it has a space before the actual email address.

To Fix: edit the contact details, removing the hidden 'space' before the email address.

Have you copy pasted a list of names from a text file ? If the string is too long, it will separate into multiple lines with <cr><lf>'s. They are creating the double-quotes. To fix: Remove the <cr><lf>'s Suggest you consider using the thunderbird address book as it can be exported as a .csv which can be opened using Excel and can also act as your backup.

Thank you so very much. I will try all these suggestions until I get it right. I'm 68 years young and still learning.

I know you didn't ask for it, but I've put together a bit of info which may be of use.

Thunderbird has address books eg: 'Personal Address Book'

If you add contacts into the Address Book, then you can easily add them to TO fileds using the Contacts Sidebar.

If you have an email from someone, open email to read. It will show you the 'From' email address/person with an outlined star next to it. Click on the email address and a pop up offers options. Choose 'Add to address book.' Contact by default is put in the 'Personal Address Book'. The outlined star will turn yellow to show person is in your address book.

You can then access the 'Address Book', select the 'Personal Address Book', double click on the contact to open a window to edit the details. Complete some sections like the name or display name etc. Click on Ok.

In a new 'Write' message. enable the 'Contacts sidebar' select the 'Personal Address Book' a list of contacts will be displayed.

select contact and click on eg: 'Addto To' or 'AddtoBcc' button as desired. It is advisable to use at least one email address in a TO field, even it is only your own.

Note: 'How to select more than one and insert in one go.' Hold down 'Ctrl' key and click on various contacts to highlight serveral. then click on 'Addto To' button

If you would like to know more about 'Mailing lists then read info at this link:

• https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird

I have added images to help you to see what I'm refering to.

You're an angel. Thank you for helping me and, no doubt, others.

I would also suggest using the mail merge add-on. It is a bit of a task to learn, but it is a more elegant solution, and offes the chance to personalize the mail with things like the persons name and other special information.

I will warn that it is very picky about CSV files, it is their way or the highway. But the results are much nicer than using blind carbon copy.

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

Thank you both for helping me. Very much appreciated.