Thunderbird is a free, open-source, cross-platform application for managing email and news feeds. It is a local (rather than a web-based) email application that is powerful yet easy-to-use. Thunderbird is developed, tested, translated and supported by the folks at Mozilla Corporation and by a group of dedicated volunteers. Thunderbird gives you control and ownership over your email. There are lots of add-ons available for Thunderbird that enable you to extend and customize your email experience.
Thunderbird gives you IMAP/POP support, a built-in RSS reader, support for HTML mail, powerful quick search, saved search folders, advanced message filtering, message grouping, labels, return receipts, smart address book LDAP address completion, import tools, and the ability to manage multiple e-mail and newsgroup accounts.
An Archive feature similar to the one in GMail
Lightning fast search
Thunderbird 78.9.0 fixes:
New mail notification displayed old messages that were unread
Spaces following soft line breaks in messages using quoted-printable and format=flowed were incorrectly encoded; existing messages which were previously incorrectly encoded may now display with some words not separated by a space
Some fields were unreadable in the Dark theme in the General preferences panel
Sending a message containing an anchor tag with an invalid data URI failed
When switching tabs, input focus was not moved to the new tab
Address Book: Syncing a read-only Google address book via CardDAV failed
Address Book: Importing VCards with non-ascii characters would fail
Address Book: Some values may not have been parsed when syncing from Google address books.
Add-ons Manager did not show if an addon used experiment APIs
Calendar: Removing a recurring task was not possible
Various security fixes
The fix for bug 210148 included in Thunderbird 78.8.1 was removed. New mail notifications not showing if there were unread messages from previous notifications.
Mozilla Thunderbird 78.9.0
Mozilla Thunderbird 52.9.1
Mozilla Thunderbird 17.0.11 ESR（企业版）
Mozilla Thunderbird 3.1.20