Re: addressing emails in Thunderbird in NVDA
First, you shouldn't place multiple addresses in the address line nor should you use the cc field unless you want others to know who got the message such as in a business or organization context. If you are simply sending a message to a group of people and there is no reason for them to know who else received the message, use the BCC field. Many people object to their e-mail addresses being splattered all over the internet. Also, in such cases, place your address in the to line. That will mean that you will get a copy of the message but that is not why it is done. It is done to keep other peoples' addresses private.
There is no trick with NVDA nor should there be. Screen-readers should not provide ways of doing something that can be done well by a blind user in a program.
I don't know why you are having the problem you describe. Knowing every step you are following might allow me or someone else to know.
However, if you download and listen to this presentation excerpt, which is me explaining how to place contacts in messages in Thunderbird and control which field they are placed in, it may solve your problem as well as allow you to place addresses in the BCC field.
From: Dan Beaver
Sent: Sunday, April 03, 2016 2:40 PM
Subject: [nvda] addressing emails in Thunderbird in NVDA
I read the help page about this and it said to press enter after each
address I entered in the to: field. However, when I try to send the
email it comes back with an error and has all the email addresses as one
long string instead of using it as individual addresses.
How do I address an email to multiple people using NVDA? I realize this
may not be an NVDA issue but I am hoping there is some trick to doing
this in NVDA.