The latest version of TapirMail is now Open Source and so there's no need to contact me or pay to register.
However, the program still requires you to go through a simple registration process in order to access the full functionality of the program. Luckily it's very simple though. Simply select the registration option from the iconbar menu, enter a name (any name will do) and click OK. This completes the process.
Note that no registration key is needed and the name you enter isn't sent anywhere. The process is only required because I've not yet had a chance to remove it yet.
Eventually the code will be uploaded to somewhere like SourceForge, but I've also not had time to do this either. If you want a copy of the source, let me know and I'll be happy to provide you with a copy. The code is available under an MIT-style licence.
I hope you enjoy using the program and if you find it useful it would be great to hear from you.