I have not received much feedback on this, so I have not developed this further.  I may pick it back up soon.

To encourage more people to try out the add-on in Thunderbird I will send dogecoin to anyone who sends me an email to emailCoinFilter@gmail.com.  You will get an auto-response saying it went to my bulk mail folder, but I will be checking that too.

The plugin sends a reply to people that are not in a white list (people that do not need to send coin).  Since the default amount is a fraction of a cent, I can imagine that most would just attach coin to every email. This initial plugin is to see if people think this is worthwhile. Future development could include an email gateway or email service that has this filter built in. And yes you need the Dogecoin client running with a rpc user and password.

I should have mentioned that it is a Thunderbird plugin

I am excited to announce emailCoinFilter, a new system using cryptocurrency to help filter spam from your inbox. Differentiating between junk email and desired email has always been a challenge. With emailCoinFilter you can set an coin amount for people to reach your inbox. And similarly if you want to ensure your email gets to others inbox you can attach a transaction of cryptocurrency. You can also add emails to a white list which will not require their email to have cryptocurrency and you can add to a black list which will always send the email to the bulk mail folder. If you find after a while that you are still getting too many emails to your inbox, you can always raise the amount of coin required. With this, you are the recipient of the postage in the email. Over time you may collect enough postage to pay for your time you spent reading messages in your inbox.

I imagine most people will not want to send much coin with an email, and most coins have anti-dust fees in place.  I have chosen Dogecoin network for sending and receiving coin.

Keep in mind this is Beta code.  I have tested it, however I would not use an account with a lot of coin in it.

Try it out at https://github.com/emailCoinFilter/emailCoinFilter