Inbox, the email startup founded by Dropbox and MIT alums offering modern APIs that allow developers to build new applications on top of email’s aging underpinnings, is today taking steps to make it even easier for developers to get started with the launch of open source email apps. The company is also announcing the pricing for its hosted version of the Inbox API for the first time publicly.
The company, co-founded by MIT alums Michael Grinich, previously an engineer at Dropbox and designer Nest, and Christine Spang, an early Linux kernel engineer at Ksplice (acquired by Oracle), came out of stealth shortly after Google revealed its Gmail API, which likely worked to its advantage. Though similar in concept – both are designed to reduce developers’ reliance on older protocols like IMAP – Gmail’s API, obviously, only works with Gmail. Inbox, however, now works with Gmail, Yahoo, Hotmail/Outlook.com, Microsoft Exchange, and pretty much every other email service out there – as the company touts on its Features page, “From ActiveSync to Zimbra.”
In addition to the expanded support for email service providers, Inbox also added calendar APIs a few weeks ago, which is helpful for developers building email applications that tie into calendaring.
Grinich is passionate about the problem Inbox wants to solve – in fact, he even wrote his thesis at MIT on email tools, and discovered how difficult it was to add features to email apps. The biggest issue, he realized explained to us, was the “underlying plumbing” – IMAP, MIME, character encodings, etc. – things that Inbox fixes for developers.

Hosted Version And Pricing 
Since its debut earlier this summer, Inbox has invited a number of testers to the Inbox Developer Program, which is $99 per year and allows the developer to sync up to 10 accounts. This serves as a staging ground, where apps can be built and tested with the hosted version of the API.
With the hosted API, developers don’t have to worry with syncing and storing mail data – Inbox handles it. The hosted version also includes full support for Microsoft ActiveSync, including contacts and calendar – a feature set aimed at developers targeting the enterprise markets.
Now the company is disclosing its pricing structure for this service – it’s $5 monthly per account, and developers can sign up or cancel at any time. This includes unlimited API requests, support for Gmail, Exchange, Yahoo and dozens of other providers, and no other fees. A 30-day free trial is available for testing, with some limitations: the app must be free to end users during this time, and old mail is synced slowly at 1 message per minute. (New mail is synced normally). An upgrade removed this forced slowdown.

Open Source Mail Apps
Inbox is going one step further than simply offering up an API platform, today – it’s also rolling out open source “scaffolds” for developers to build rich email apps on top of. “This is huge, and will usher in a new wave of innovation for email,” says Grinich. “Say goodbye to hacked-together Gmail/browser extensions.”
There are two scaffolds available at launch: HTML5 and iOS. The company explains it built these first because it’s what its team knows the best, but would love help expanding to other platforms, like Android. The scaffolds will get new features weekly, but at launch on iOS, Inbox has a mechanism that seamlessly merges new API requests with cached data, it claims. And the HTML5 version is “a modern standalone single-page app, running entirely client-side via AngularJS and the Inbox.js library.”
Inbox also has an open source repo here on GitHub, that has over 1,500 stars.
