Rated 5 out of 5 stars

The only function I regularly used in Outlook and missed in Thunderbird was the possibility to specify a time and date when to send a message. An Add-On with the name "Send Later" was quickly found and installed.

Now that I tried it, I find the name "Send Later" to be a massive understatement of this app's capabilities. While it gives you the possibility to easily send emails at a later stage (and with a lot more comfort than Outlook's function at that!) , it allows you an immense level of customization.

You want to send every email with a delay of 15 minutes, in case you change your mind? No problem. You want to send your email on a specific time and date? No problem. You want to send your email immediately if it's business hours or else the next day? No problem. You want to send an email only when it's full moon? Well, not built-in, but with a bit of JavaScript you can do just about anything. :)

Really, great app. Thanks to the dev for making this available for free and open source.

This review is for a previous version of the add-on (6.1). 

*blush*