Stop Ignoring Reply:To Requires Restart
Default "Reply" functionality pays attention to "Reply-To" in original email
Add menu commands for replying to multiple messages at the same time.
ThunderHTMLedit Requires Restart
Thunderbird HTML editor. This add-on adds a HTML tab to the composition window where you can see and edit the HTML source of the message.
Send Later Requires Restart
True "Send Later" functionality to schedule the time for sending an email.
MEGAbird Requires Restart
Add MEGA support to Thunderbird's Filelink feature.
SmartTemplate4 Requires Restart
SmartTemplate4 offers an easy way to automatically create customized replies by auto-inserting various mail headers. Templates can be created for every account as well as for the default (all email accounts). Also supports the Stationery Add-on.
CategoryManager Requires Restart
Category manager for Thunderbird contacts, also allows to send an email to all members of a category (categories can be used as contact groups).
As-you-type phonetic conversion of text from one alphabet to another, as well as transliteration/detransliteration of selected text anywhere within documents. Supports multiple languages and custom transliteration schemes.
Address bulk copy （アドレス一括コピー） Requires Restart
Thunderbird は Outlook のようにアドレス全選択からの「一括コピー」ができません。
Mail Merge Requires Restart Featured
Create and Save or Send Multiple Individual and Personalized Messages from a Draft
Remembers the language you use with a person or group of people, and switches the spellchecker language automatically for you next time. You do not have to do it manually any more. It remembers and switches it for you.
ThunderPEC Requires Restart
ThunderPEC semplifica la gestione della Posta Elettronica Certificata (PEC) e delle comunicazioni PCT e FatturaPA in Thunderbird.