Displayname is what appears in the email address in to: Is yours blank?

It's not blank. It has first name, last name showing. Emails I receive, show first name, last name followed by their email address but when I create an email, it's just the email address.

It's not blank. It has first name, last name showing. Emails I receive, show first name, last name followed by their email address but when I create an email, it's just the email address.

Emails you receive - the sender may have inserted the display name prior to the email address.

You mention 'First Name, Last Name' but you were asked specifically 'Display name' In Address Book Select the contact Click on 'Edit' Is that 'Display name' field empty? If yes, Enter their name in 'Display name' field Click on 'Save'

All my address book entries have first name, last name in the 'Display name' box.

I discovered the solution. When I converted from Outlook 365 I let Thunderbird convert by previous address book. The new entries looked correct, First name, Last name and Display name but the Display name didn't show in new emails as I said. However when I go into one of the new address book entries and just click Save, things work fine for that entry. I don't need to change anything, just click Save so maybe the conversion process needs something. I just need to Save all my entries.