This decentralized email application is a prototype of how a messaging system would work on a blockchain. No human power on this planet can block your account/address from the chain. You have the power to do what you want on the internet. Neither can somebody else keep a check on your messages unless you give them your address and the password you are using for sending and receiving emails.
Emails usually involve sending attachment files/photos, but storing them on a blockchain is not possible because of the storage issues. Hence for sending files via the messaging Dapp we make use of the Interplanetary File System(IPFS). If one wishes to send a file, he/she shall upload the file and carefully copy the link that is returned after uploading in the email body. Another challenge is of the response time. Communicating with blockchain often takes some time since it solves a cryptographic puzzle to find a nonce value that adds the block to the chain. This is a problem of scalability, Blockchain has always had a problem with scalability.