Like most email clients, Mozilla Thunderbird has a very useful auto-complete function which allows you to choose from previously-used email addresses when composing a new message. However, removing entries from this list is not as easy (or obvious)Â in Thunderbird as it is in Microsoft Outlook, for example, where all you have to do is press the DEL key when the auto-complete list pops up.
Instead, Thunderbird seems to store the auto-completion list in a section of the Address Book called Collected Addresses. To remove an entry you have to:
- Click the large Address Book button in the main (Mail Filter) toolbar
- Select the Collected Addresses group
- Locate and delete the desired addresses from there
Source: mozillaZine Forums