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

Thunderbird, Postbox

Send & Receive

Send and receive messages

Send all messages in the outbox and get all new messages.

Compatibility: Thunderbird, Postbox SeaMonkey

Send Without Save

Send message without saving a copy

Send message with out saving a copy to the sent folder. If you want this as the permanent behaviour, there is an option in account settings under 'Copies & Folders'

Compatibility: Thunderbird, Postbox SeaMonkey

Tasks In View

Toggle Tasks in View

Toggle the Task in View panel in Sunbird.

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 Tasks

Toggle the task bar

Toggle the task bar between visible and hidden.

Compatibility: Thunderbird, Postbox SeaMonkey

Unread Threads

View Unread Threads

View threads that you have not read yet.

Compatibility: Thunderbird, Postbox SeaMonkey

Watched Threads with Unread

View Watched Threads With Unread

View watched threads that have unread messages in them.

Compatibility: Thunderbird, Postbox SeaMonkey