Review for PennyPost by Adrian Zaugg
Rated 5 out of 5 stars
The idea behind this add-on is good and it should get in the focus again: With abused IoT devices sending spam nowadays hashcash is an effective measure (amongst others) for spam detection.
The plugin works in recent TB 52.4.0. When setting up, don't forget to place the icon for stamping messages onto your message composition window.
To create your own collections, you must have a Mozilla Add-ons account.