Fortunately, Mozilla Thunderbird remembers them, and when you start typing a name (or address), it is completed automatically. Still not ideal for adding 20 recipients to an email you forward — and you don't want to set up a group?
Mozilla Thunderbird has a trick up its toolbar for this situation, too: the Contacts sidebar. And if you're missing an Add to Bcc: button, turn to the context menu.
Add To, Cc and Bcc Recipients Easily in Mozilla Thunderbird
To add recipients swiftly in Mozilla Thunderbird:
- Click Contacts in the message's toolbar.
- Optionally, select the desired address book or use search to locate the desired recipients.
- Note you can only search one address book at a time.
- Highlight all people you want to add.
- To add them to the To: field:
- Click the Add to To: button.
- To add them to the Cc: field:
- Click the Add to Cc: button.
- To add them to the Bcc: field:
- Click on one of the recipients with the right mouse button.
- Select Add to Bcc field from the menu

