SpringEmail: How to design a payable blockchain secure mailbox?

1 Introduction to SpringMail and BiSMTP Protocol

About Chunyou: Chunyou hopes to greatly improve the usability of cryptocurrency and expand the user base and usage scenarios of cryptocurrency through the integration of Blockchain's protocol and the existing Internet Mailbox Protocol (SMTP), to realize Qtum's vision of value transfer protocol and achieve a seamless payment experience on the Internet. In Qtum's white paper, Qtum innovatively proposed the concept of value transfer protocol (VTP protocol: Value Transfer Protocol), which embeds smart contracts into the protocol layer and combines the existing standards of the World Wide Web to achieve a blockchain payment protocol that integrates the existing TCP/IP protocol stack. This payment protocol will bring more intelligence and more business possibilities, and achieve a seamless Internet payment experience.

About BiSMTP protocol: (Blockchain integrated Simple Mail Transfer Protocol), a simple mail transfer protocol based on blockchain, is a fusion protocol proposed by the Qtum team that integrates blockchain technology and existing mail protocols. Through this protocol, users can use mailboxes to send and receive small amounts of digital currency. This protocol will expand the existing SMTP protocol stack, send and receive cryptocurrencies through a markup language, and expand the functions of the mail server so that the mail server can process this markup language, thereby realizing the sending and receiving of small amounts of digital currency through emails, and can be widely used in payment scenarios on the Internet.

When using digital currency, users usually need to download a wallet client or use an online custodial wallet. Downloading a wallet client means that users need to download the entire blockchain data at the same time to manage their property normally. Custodial wallets can provide users with more convenience, including avoiding users from downloading increasingly long blockchain data, as well as more online extension functions.

We are here to provide users and the community with another possibility, which is to complete the digital payment function without the need for users to download the entire blockchain. We provide users with a digital wallet based on the traditional email experience, and provide the community with an email solution based on the Qtum network.

SMTP is the classic email office protocol of the Internet. Our goal is to implement the functions of the classic email office in the distributed Qtum network, and further abstract the classic email box and expand it into the BiSMTP protocol.

2 Redefine the mailbox

A traditional email address, such as [email protected], consists of two parts:
 Email ID (account): spring
 Email server name: coco.info
The mailbox ID is valid only for the domain coco.info. We will inherit this standard address format, but its meaning will be redefined while ensuring compatibility with traditional email boxes and traditional email clients.

In the Qtum network, the email address has the same format as above, but the meaning of each part has changed. For example, [email protected] consists of the following two parts:
Chain address : 1PkyncFDsXmcg6pnPUvNJWougztWejAdVe
Access domain name : node.example.com
Assume there are two chain addresses:

①1KvwTxFqJSSjztyEN3LLmLDWr4xVZtGk96
②1PkyncFDsXmcg6pnPUvNJWougztWejAdVe

Wang Jun has chain address ①, and Li Jun has chain address ②. Without downloading any Qtum wallet client, Wang Jun wants to send information (assets) to Li Jun. We can create the following email in the network:
From: [email protected]
To: [email protected]
Subject: Great Money for Li

Where @node.example.com represents a reachable node or Broker in the Qtum network.
A key difference between the new address and traditional email addresses is the cross-domain identification feature.

Definition: Cross Domain Identification
Definition: Distributed Mail Server

Figure 1: Network Identification

2.1 Chain Address

The chain address is what we call a wallet address. The chain address represents the actual message recipient in the Qtum network. Anyone who has an address can use it to receive emails. When a user obtains ownership of an address, it means that he or she has the corresponding private key.

Chain addresses are unique in the Qtum network, and this feature is not changed by domain. Any email sent through the Qtum network can be delivered through the chain address, regardless of which domain it is accessed from. This is a huge difference compared to classic email, but it is transparent to the classic system.

Because classic email is usually bound to a mail server domain, such as gmail.com. But in the Qtum network, the domain is more of a portal - an access domain .

2.2 Access Domain

When a user initiates an email request, the classic SMTP protocol is applied. Users usually use email clients to initiate SMTP requests, and these requests must be escaped before entering the Qtum network or forwarded directly to the recipient's email office (according to the Mail Classes Definition attribute of the email).

Nodes in the Qtum network can be responsible for receiving emails (but nodes do not have to be so), or they can be escaped and processed by Brokers that are specifically responsible for handling SMTP requests and then put into the Qtum network.
The host that can process SMTP requests and convert messages into a predetermined format (Inter-Message Format Definition) for transmission on the Qtum network (according to a specific protocol Protocol Definition) is called an access domain. Therefore, in the classic concept, an access domain is a mail server that serves traditional mail clients.

3. Network access (Interconnection)

As mentioned above, nodes in the Qtum network can be responsible for accessing emails, but considering the processing power of nodes, directly processing SMTP requests cannot be their main function. Nodes are usually scattered and uncertain. Mail services must be provided by reliable and capable hosts.

We call the component responsible for receiving SMTP requests Broker, so the host running such a Broker can be called an access domain. Broker can exist in the form of reliable services, provide email services to many customers, and escape email requests to access the Qtum network.

Service operators can register a dedicated domain name for the Broker service, such as broker.example.com, to facilitate users to configure their email clients. We can imagine that there are many access domains that exist at the same time, serving different user groups. But as long as they are connected to the Qtum network, they are actually equal.

Assume there are two domains broker1.example.net and broker2.example.net,

If you send mail to the following two addresses:

[email protected]
[email protected]

The result is the same. The people who finally received the email are all people with the address 1KvwTxFqJSSjztyEN3LLmLDWr4xVZtGk96.

Figure 2: Broker Topology Broker Topology

Broker is a crucial component in Spring Email. We will design the following operation modes but not limited to:

3.1 Broker Node Proxy

Proxy Node is a lightweight node that does not download the complete blockchain, but takes on the task of network reception and information forwarding. Implementing Broker in Node Proxy can be a good choice.

Proxy Node is a very good choice for users because it does not need to download a huge blockchain, so it is more usable, but it cannot get full functionality. It is worth noting that Node Proxy is not a Full Node. If there are too many proxies in the network, it will lead to network centralization, which is not conducive to network decentralization.

3.2 Broker Node

Broker Node is a Broker function implemented in a Full Node. For users, this is like turning on the Broker option in the Wallet Client, and other users in the local network can use regular mail clients to set the host as an outgoing mail server.

3.3 Broker Mail Server

Broker Mail Server is designed to serve more email clients and provide reliable and personalized email services.

3.4 Expanded Services

1. Wallet custody
Broker can be expanded into a reliable service and does not host wallets for users, making it easier for users to send and receive coins, even digital assets.
2. Mail service provides high availability traditional mail service.
3. Special businesses provide unique services based on their own business and make profits from them.
4. MX Service provides access solutions for enterprise-level email services. Enterprise-level email services require a lot of resource investment. We can also provide access solutions for existing enterprise email service providers.

4. Email delivery

4.1 Classic Mode

While taking into account the classic email post office protocol, we extended it to the Qtum blockchain network. This enhances the email sending function and expands the concept and application domain of mailboxes, making it more practical and accessible. To summarize this enhancement and expansion, there are at least the following obvious changes:

1. • Mailbox is no longer limited to a certain mail server

2. • The mail delivery path becomes dynamic and has multiple possibilities

3. • Emails will be encrypted and signed so only the recipient can read them

Users usually use a compatible mail client to compose mail. The client initiates a network session with the mail server through SMTP, and the mail is delivered to the server where the recipient's mailbox is located through the server. The server determines the recipient's account and distributes the mail to his mailbox. This is the mail sending process of the classic SMTP email office (classic mail sending diagram).

Figure 3: Classic Email Delivery Path

The classic email sending model has some obvious shortcomings:
• Mailbox centralization, its availability is completely determined by the mail server. Classic email boxes are limited to the domain they are in. Usually, if the service provider does not provide multi-domain support, users cannot use the same mailbox in different domains. Of course, users can choose to register multiple mailboxes in different domains using the same mailbox (this is not what we are concerned about discussing).

• Emails are usually not encrypted, and signing requires special tools (such as GPG, PGP) which usually also requires special support from the email client.

• Email services are regional. Take Gmail as an example. Although it has powerful server support, not everyone on the planet who can use the Internet can use Gmail.

• Mailbox servers may be unreachable. In some cases, mail servers cannot be well connected to each other, which makes it difficult for mailboxes on two mail servers to communicate with each other, making it impossible for users to send mails to certain mailboxes.

4.2 Distributed

Distributed mail delivery is an important change to the classic mail system, but this change is transparent to the mail client. Distributed mail delivery changes the path of mail delivery to the recipient.
Assume Alice and Bob have the following chain addresses respectively:
1: 1PkyncFDsXmcg6pnPUvNJWougztWejAdVe
2: 1KvwTxFqJSSjztyEN3LLmLDWr4xVZtGk96

Alice has access to Broker 1, and Bob has access to Broker 3, so they can send emails using the following email addresses:

3:[email protected]
4:[email protected]@com

Alice accesses Broker 1 through address 3 to send an email to Bob. Broker 1 does not know how to reach Bob, so it will ask the Qtum network for the network information of Bob's chain address 2 (such as the network address of Broker 3). After finding the network information, Broker 1 will initiate a conversation with Broker 3 and send the email. Broker 3 further notifies Bob of the email. (Distributed email sending diagram)

Figure 4: Distributed Email Delivery Path

5. Email Storage

Email is not instant communication. To ensure that mail is not lost, we must store user emails.

5.1 On-chain storage

When saving emails to the blockchain, the following issues must be carefully considered:
Mail costs Storing mail within the chain must pay higher fees to avoid abuse.

The total email byte size must be strictly limited.

5.2 External Storage

It is up to the Broker to decide how to store emails, and the Broker can even charge users for this.

It is up to the Broker or the user to decide how to store the emails. There may be the following situations:

Broker Hosting Email

Similar to the classic Mail Server, Broker allocates storage space to users and can charge service fees to users based on their business.

User-friendly mail storage

Users can also choose to run 坲坫坥坥 themselves and configure their own storage method. For ordinary users, this is not an easy task, because the 坲坫坥坥 must be kept online all the time to avoid losing emails.

6Backward Compatibility

6.1 Mail Client

Traditional email client

- Traditional mail sending and receiving

- Available auxiliary tools support coin transfer

Broker hosted mail client (WebMail)
- All advanced features are well integrated · Dedicated mail client (development)
- All advanced features and Wallet can be integrated

6.2 Interaction with Traditional Mail Servers

7 Security Concerns

1. DDoS

2. · verify

3. Spam prevention

4. Policy impact (emails traveling through distributed networks can break firewalls)

Official disclosure: In order to solve the value transfer protocol based on blockchain technology, the Qtum team will later announce the second community project: Qloha. We hope Qloha will bring a different feeling to everyone!

Developers and users interested in the first community project can also send an email to [email protected] for more information. The Qtum Foundation will also launch a series of incentives to encourage everyone's participation.