Message Composition

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Send Later

True "Send Later" functionality to schedule the time for sending an email.

Rated 5 out of 5 stars (267)
110,274 users

Mail Merge

Create and Save or Send Multiple Individual and Personalized Messages from a Draft

Rated 5 out of 5 stars (236)
71,822 users

Grammar and Spell Checker — LanguageTool

Check your emails for spelling and grammar issues

Rated 4 out of 5 stars (39)
69,831 users

Signature Switch

Switch the signature on/off or choose a new one from your predefined set.

Rated 4 out of 5 stars (310)
51,455 users

FileLink Provider for Dropbox

Uploads your large attachments to your Dropbox instead of sending them by email. This uses Thunderbird's FileLink feature.

Rated 4 out of 5 stars (24)
49,637 users

FileLink provider for Send

Securely encrypt and upload large attachments to any Send service instance (formerly Firefox Send).

Rated 5 out of 5 stars (17)
47,810 users

Owl for Exchange

Allows you to use your Exchange and Office365 email account with Thunderbird using Outlook Web Access (OWA).

Rated 5 out of 5 stars (213)
43,996 users

Textmarker

Highlights selected text when composing emails. Default colour is yellow - other colours are available via Options.
(Works only during writing an e-mail, i.e. only in the compose window.)

Rated 5 out of 5 stars (36)
40,366 users

*cloud - FileLink for Nextcloud and ownCloud Featured

Upload large attachments to your Cloud and send the link by email

Rated 5 out of 5 stars (54)
36,620 users

FlexConfirmMail Stable

Confirm mail address and attachments based on flexible rules.

This is enterprise edition with less updates. Another edition for regular users:
https://addons.thunderbird.net/thunderbird/addon/flex-confirm-mail/

Rated 4 out of 5 stars (11)
24,101 users

Emoji

Add emojis to your e-mails.

Rated 4 out of 5 stars (64)
23,782 users

Check and Send

Check the message contents and addresses before you send the message...

Rated 4 out of 5 stars (50)
22,276 users

Shrunked Image Resizer

Make your photos smaller, so they don't take forever to email.

*Shrunked Image Resizer is no longer maintained.*

Rated 4 out of 5 stars (89)
11,983 users

FileLink Provider for Box

Uploads your large attachments to your Box instead of sending them by email.

Rated 3 out of 5 stars (13)
11,721 users

ReplyWithHeader

Outlook style headers and few goodies for Thunderbird.

Rated 5 out of 5 stars (96)
10,597 users

Simple Mail Redirection

Allows you to resend (also known as redirect) email messages.
Uses 'cardbook' if installed

Bases on the add-on 'Mail Redirect' by Onno Ekker and Pawel Krzesniak

Please see the support page on how to use and why it sometimes does not work!

Rated 5 out of 5 stars (38)
8,510 users

BorderColors D

Shows a colorful border around the "New Message" window, so you can tell different identities apart.

Builds on the original BorderColors and the "GT" version, adding different border styles.

Rated 4 out of 5 stars (35)
7,808 users

CategoryManager

Category manager for Thunderbird contacts, also allows to send an email to all members of a category (categories can be used as contact groups).

Rated 5 out of 5 stars (26)
6,508 users

Identity Chooser

Identity Chooser helps you to always use the correct identity when composing a new email.

Rated 4 out of 5 stars (149)
5,869 users

Emoji

It permits just with a single click to copy an emoji.
There is a search-box and the "Most used emojis" section (the first one).

If you want to send feedback or report bug, please contact me

Rated 5 out of 5 stars (14)
5,823 users