These are a ready make selection of some of the most popular buttons from the Custom Toolbar Button Maker

Thunderbird, Postbox

New Task

Add a new task to the calendar.

Add a new task to the calendar.

Compatibility: Thunderbird, Postbox SeaMonkey

Not Junk

Mark the selected messages as not junk

Mark the selected messages as Not Junk.

Compatibility: Thunderbird, Postbox SeaMonkey

Reply to Sender Only

Reply only to the sender of the email

Reply only to the sender of the email.

Compatibility: Thunderbird, Postbox SeaMonkey

Rewrap

Rewrap

Rewraps the message text

Compatibility: Thunderbird, Postbox SeaMonkey

Threads with Unread

View Threads With Unread

View only the threads in the current folder that have unread messages.

Compatibility: Thunderbird, Postbox SeaMonkey

Toggle Starred

Toggle Starred Status

Toggle the starred status (look for the star next to the message).

Compatibility: Thunderbird, Postbox SeaMonkey

Account Settings

Open account settings

Open Account Settings in Thunderbird.

Compatibility: Thunderbird, Postbox SeaMonkey

Account Setup

Run wizard to setup a new account

Run Account Wizard to set up a new account in Thunderbird.

Compatibility: Thunderbird, Postbox SeaMonkey

All Threads

View All Threads

View all the threads in the current folder, not just unread or some other sub set.

Compatibility: Thunderbird, Postbox SeaMonkey

Detach Attachments

Detach All Attachments From Message

Detach Attachments from an email.

Compatibility: Thunderbird, Postbox SeaMonkey