Two years ago, Google promised to “make your phone your wallet.” But it hasn’t delivered, largely because phone manufacturers and wireless carriers have been wary to sign onto the service, known as Google Wallet.But Google may have just found a creative way into mobile payments that doesn’t require any other companies to cooperate: email.Google announced that it will gradually allow adult Gmail users in the US to attach money to their emails the same way they might attach documents, images, and other files. Transactions are free for users who link their bank accounts directly to Google Wallet; using a credit or debit card costs 2.9%. There’s a limit of $10,000 per transaction.Sending money over email is one of those incredibly simple ideas that hides how profound it could really be.As previously conceived, Google Wallet involved waving certain NFC-enabled Android phones in front of receivers installed at select businesses. Or you can download an app to transfer money, which is how competitors like Venmo and eBay’s PayPal work, too.All of that is downright cumbersome compared to the simplicity of sending an email, which could help introduce many more people to mobile payments. Google is the world’s largest email provider. Think of how SMS-based money transfers allowed mobile payments to spread quickly in the developing world. Gmail is, in a sense, the SMS of developed economies.Google can also help solve another point of friction with mobile payments, which is that both sides of the transaction need to have accounts with the service handling the money. The same is true for Google Wallet transfers, even over email, but having a Google account is way more common than having an account with, say, Venmo or PayPal. Google may be the closest thing the world has to a universal bank.That is, until alternative currencies like bitcoin—which don’t work that way and allow for more seamless transactions—start to gain mainstream adoption.