blunderdelay

usage.html

Configuration

In your extension manager, you can choose to edit BlunderDelay settings. Settings include:

When you are ready to queue your outgoing message, do not click Send Now since this will do exactly that and BlunderDelay will have no effect. Use the Send Later command in the File menu so your message queues in the Unsent Messages folder until BlunderDelay next activates.
To make this operation more convenient, Thunderbird does have a Send Later toolbar button, but it is only available in offline mode. To make it available in online mode also, install an extension such as MagicSLR.
If you want to return to finish a message later, be sure you use Save rather than Send Later if that was your habit. With BlunderDelay active, Send Later is no longer a permanent parking place.
If you decide to change a message already in queue, Thunderbird will not allow you to actually edit it merely by double clicking it. You will have to right click and select Recall to make changes. This will remove the message from the queue and open it for editing as if new. WARNING: This command is intended for use in your Unsent Messages folder. See known bugs below.
The send interval is regular and not coordinated at all with when you write your message. So like catching a bus, if you queue your message 30 seconds before scheduled departure, this will not leave you much time to review your message. Eventually I hope to make messages hold for a fixed amount of time relative to when they were queued.

BlunderDelay only operates while the main Thunderbird window exists. At least on Mac OS X, it is possible to quit the main window (using Hide) even though Thunderbird continues running in the background. When you do this, BlunderDelay does not run in the background, but instead will disable until a new Tbird window is created. Minimizing the window will not have this effect for either Mac or Win. So this may be an issue only for mac users.
The Recall command is intended for use in your Unsent Messages folder, but nothing yet prevents you from applying it in other folders where it will have the unintended result of recreating a received message as if it were sent by you.
Use of Thunderbird's Send Later command fails to delete your message from the drafts folder. So, if you saved a draft before sending (or have autosave enabled in your preferences), using BlunderDelay will retain copies of your sent messages in your drafts folder. This is the manifestation of bug #314009 in the core Tbird code. If you observe this bug and it bothers you, register with Bugzilla and vote for the bug. A patch has already been written so it's just awaiting application to the trunk, I think.