It is possible for an email address to have an associated user-friendly display name. For example, the email address email@example.com might have an associated display name of John Smith.
There are two places where a display name can be associated with an email address:
Suppose you receive a message from firstname.lastname@example.org. As you look at the list of email messages in your inbox, what you see in the From column for the message will depend on whether or not there is a display name for email@example.com in the message itself and/or in your address book.
Setting the Display Name in a contact in your address book
Note that it is useful to have contact info in your address book, because the contact info contains (or can create) a display name for messages that you send. When you click on an address book contact to send a message, the display name that you have in your address book is sent along with the email address.
If you receive an email message from someone who is not in your address book, and you use the message to add the sender's email address to your address book, if the message contains the sender's display name, then that display name is added to the address book. If the message has no display name, you can manually add a display name to a contact in the address book.
And of course you can manually add, remove, or edit a display name for any contact in the address book.
Where Thunderbird shows display names
The display name for a message is displayed in two places in Thunderbird:
The rules governing the display of the display name are different in a message list (for example, the list of messages in your inbox) and the message display.
In the message list:
In the message display:
In short, the message list will always use the display name from the address book (if there is one) but the message display will never use the display name from the address book. Because of this difference, the display name in the message display may be different from the display name in the message list.
Here is an example. We have received an email message from email address firstname.lastname@example.org. The message contains the display name CineNews. Our address book contact specifies that the display name associated with email@example.com is Front Row Centre.
Because our address book contact specifies that the display name associated with firstname.lastname@example.org is Front Row Centre, Front Row Centre is what we see in the message list.
Because the message contains the display name CineNews, CineNews is what we see in the message display.
To always use the display name from the message header, go to Thunderbird > PreferencesTools > OptionsEdit > Preferences > Advanced > Reading & DisplayDisplay > Advanced and uncheck Show only display name for people in my address book.
You can specify this preference for individual contacts by editing the contact in the address book and unchecking Always prefer display name over message header.