ChainInBox

ChainInBox: Send Crypto Like You Send Email

Imagine if sending crypto was as easy as sending an email. That’s exactly what ChainInBox does — it’s like adding a magic “Send Money” button right inside your Gmail.

No more copying long wallet addresses, switching blockchain networks, or stressing over gas fees. Just type, click, and done.

So, what can you do with ChainInBox? You can send money to anyone across different blockchains — Ethereum, Arbitrum, Base, Optimism — and any Avail-supported network without worrying about which network they use. ChainInBox figures it all out for you. Creators can also campaign emails to their audience and include instant payment links, enabling subscriptions, donations, or product sales directly in the inbox.

Startups can pitch directly in your inbox. You can invest in them instantly with USDC from any chain you have it on. Freelancers and teams can get paid globally, without banks, wires, or confusing crypto transfers.

How does it work? When composing an email, just enter the recipient’s email or wallet address. You’ll see a new “Pay with Avail” button — type something like “50 USDC to Optimism” in the subject, hit send, and the payment is processed instantly.

Seamlessly integrated into your inbox, Avail Nexus handles everything behind the scenes — bridging assets across blockchains, managing gas fees, and ensuring your payments reach the right wallet, all without leaving your email.

Every transaction runs on secure, automated smart contracts optimized for lending, limit orders, mail-linked storage, USDC escrow investments, and yield farming, making blockchain finance simple and reliable.

Why is this such a big deal? Crypto payments used to be a mess — you had to guess the right network, bridge tokens manually, pay multiple fees, and pray you didn’t paste the wrong address. ChainInBox changes that. Transactions take minutes, not days — and you keep those extra 3–5% in fees in your own pocket.

It’s already live and real. You can check verified blockchain transactions like Intent #1106, where someone sent USDC from Ethereum to Optimism in one click, or Intent #1084, where an investor funded a startup on Base Sepolia using tokens from another chain. Our smart contract (0x1302C9F621046A2dc56F63dDc9A7A2FBBe8fE71c) even handles investment escrow automatically — so founders get funded, and investors stay protected.

Gmail Integration & Frontend We built ChainInBox using Next.js 15, React 19, and TypeScript, creating a Chrome Manifest V3 extension that integrates directly into Gmail's layout. Content scripts monitor emails and inject native-looking buttons like "Send Payment" or "Contribute" using Tailwind CSS 4 to match Gmail's design. The extension detects payment requests through regex pattern matching, extracting wallet addresses, amounts, and chain specifications, then opens pre-filled popup windows via window.postMessage APIs.

Avail Nexus SDK Integration Our Next.js backend connects with the Avail Nexus SDK, leveraging three core widgets: TransferButton for cross-chain payments, BridgeButton for token bridging, and BridgeAndExecuteButton for combining bridging with smart contract execution in single transactions. We used Viem 2.38 and Wagmi 2.18 for type-safe Ethereum interactions, handling everything from cross-chain swaps and liquidity routing to unified asset management across 12+ blockchain networks.

Wallet Connectivity & Storage We implemented a hybrid wallet system supporting MetaMask/WalletConnect for traditional users and Magic.link for email-based Web3 authentication. Chrome's storage API manages user preferences, background service workers handle extension lifecycle events, and injected scripts (nexus-ca.js bundled via esbuild) embed the Nexus SDK into Gmail's page context, allowing access to window.ethereum while maintaining security boundaries.

Smart Contract Architecture We developed five Solidity ^0.8.20 contracts deployed on Base Sepolia: USDC Investment Escrow (0x1302C9F621046A2dc56F63dDc9A7A2FBBe8fE71c) with OpenZeppelin's ReentrancyGuard and SafeERC20, MailVault for time-locked transfers, LendingPool with per-second interest, LimitOrder for swaps, and YieldFarm for staking. Avail's intent-based architecture allows users to invest from any of 12 chains without manual bridging—Avail automatically routes liquidity and manages gas fees.

Avail Intent Embedding Innovation One of our coolest hacks was embedding Avail intent links directly into emails. When transactions complete, we insert rich HTML snippets with Nexus intent IDs and blockchain explorer links into the email body, letting users trigger and verify real blockchain transactions instantly from their inbox. Our build pipeline compiles everything with esbuild into a production-ready Chrome extension where blockchain complexity is completely abstracted—users just click buttons in Gmail.