Last month, Ryan Hoover had a great post about building email into your startup first, before moving on to other platforms. His awesome points:

• Email lets you validate ideas quickly
• Since email is async, you can fake functionality with manual processes
• Forces focus
• Email is a part of users daily habits
• Email is ubiquitous
• You can use email to upsell users to other platforms when you’re ready

Posterous was the ultimate email first product. I started the project because I wanted to email photos from my iPhone to my blog. I wrote thousands of lines of email code, which posted to my Blogger blog, before I ever wrote a line of web code.

There are a few other reasons why I think email an amazing platform to build on top of:

• Email has identity built in. Email is identity. Whether you’re sending or receiving email from users, you don’t need a login system. Posterous was able to completely eliminate signup from our flow.
• Email is mobile. It’s on every device, including super low end feature phones. Even people in developing countries on slow internet connections can use email.
• Email isn’t blocked in China. You open your service up to another billlion users.
• Email is integrated in all the apps you use. You can email photos from iPhoto, or a link from Safari, or a Tweet from Twitter.
• Email supports rich content. You can send photos, documents, video, audio, and any arbitrary attachment. There’s nothing email won’t transfer.
• iPhones will send email in the background. If you’re sending a video and your internet is slow, the iPhone will keep uploading while Mail is in the background.
• Users get notifications instantly, on all devices, without managing extra notification permissions or settings.
• So easy, your mom can do it.

Email is a powerful and flexible platform used by billions of people around the world. Start your company with email first in mind, and integrate it deeply in everything you do.