Square has just released the simplest way to send money to anyone online. And yet, there’s no guarantee it will be a success.With Square Cash, anyone with a debit card can send money to others simply by crafting an e-mail, putting an amount in the subject line, and hitting send. After your first Square Cash transfer, it asks you to enter your debit card information. For the recipient, they just need to plug in their debit card info to receive the money.The key here: You or the recipient of the cash don’t need to sign up for any special accounts, and it doesn’t charge any surprising fees. The money also goes directly into a recipient’s bank account in 1 to 2 days, rather than sitting in a holding account (which typically takes up to 4 days to transfer). At this point, transactions are limited to $2,500, a Square representative tells me.Square has been testing the feature since May, but now it’s finally open to the public. It’s also unveiling a Square Cash iOS and Android app, which basically serve as a fancy way to send a Square Cash formatted e-mail.While it’s shockingly simple, Square Cash’s ease-of-use could also be a turn-off for mainstream users who aren’t as familiar with the company’s brand. E-mail isn’t typically recognized as a secure medium, and while Square claims it has systems in place to prevent spoofing (according to an interview with The Verge), it will likely be tough for users to accept sending money through the same e-mail account where they receive thousands of spam messages every week. Square Cash requires a new level of faith that average users will have to accept.At the same time, Square Cash’s simplicity and convenience seems like the ideal competitors such as PayPal and Venmo have been aiming for. Earlier this year, Google also released a new Google Wallet feature that lets you send money through Gmail, but that wasn’t anywhere near as simple as Square’s offering.Sending money to others online isn’t new — it was PayPal’s defining feature when it launched in 2000, and since then we’ve seen a slew of competitors enter the space. But sending money with PayPal and other services is typically a multistep process: You have to sign up for a free account and link it to your bank account. To its credit, PayPal has vastly simplified its peer-to-peer money transfer feature over the past year — it’s now a highlighted feature in the company’s mobile apps.For all of the criticism PayPal receives, there’s a certain amount of irrational comfort seeing funds enter your account and having a history of transfers available at a glance. That’s something that you don’t really get with Square Cash. Since it doesn’t connect to your existing Square account, the only record you have of the transaction is your e-mail history, which could be problematic if there are issues with transactions.With Square Cash, we may end up seeing how too much simplicity could end up being a bigger problem for usability.