[eb0la]

The biggest problem of using a blockchain for email is that you will need to have a copy of the blockchain to record all the transactions (mesages) sent in the past.

If you do this in the European Union, you are shooting yourself in the foot.

Why?

First because data protection laws dictate anyone can oppose against the treatment of his/her data in your systems. Email is considered personal information here. If you put email in a blockchain you cannot effectively remove data from it because it breaks the whole chain of signatures.

Maybe you could do something like cyphering the data before dumping it in the blockchain, and using a smart contract or inserting a special record to make it unavailable (not erased, but made not accessible).

Second, you cannot distribute / share personal data as you want. In some countries -like Spain- you need a signed autorization by the Director of the Data Protection Agency.