Posterous Goes Bare: Shows Us All Its Stats

I like to write about actual numbers, but start-ups are usually reluctant to give them up, preferring to blab about growth percentages and fuzzy feel-good milestones.

The lightweight blogging company Posterous volunteered to open its books recently, coughing up every product stat NetworkEffect asked for during a recent visit to the company’s oversized San Francisco Mission District office situated below a yoga studio whose clientele is way more clompy-footed than I might have thought.

The Posterous team, led by CEO Sachin Agarwal, was pimping its new groups product, launched Dec. 15, that’s kind of like a nice-looking Web interface for an email product like Yahoo Groups, turning messages into blog posts and smoothing photos and other attachments into easily viewable form. Used mostly for private communication (like a neighborhood group or a small business team), the groups tool supports users who participate by email without opening a Posterous account.

First of all, Posterous Groups is still quite small: Posterous has 12.3 million total blogs, and only 134,000 of them are groups. About 3,000 groups are created per day, or about 20 percent of total daily sign-ups.

Overall, Posterous has 9.2 million monthly visitors on its own site and on custom domains, according to Quantcast, which measures the service directly with its permission. That’s up from 6 million in September, but still quite a bit less than competitors like Tumblr and WordPress, which have 59.6 million and 517 million people, respectively.

The new groups product sends a ton of email (with user permission, and with the help of SendGrid): 230,000 messages per day. Half of Posterous group distribution is over email rather than the Web, and 30 percent of users are not registered.

As I mentioned earlier, most groups–76 percent–are private. And a quarter are for corporate groups–an alternative to business collaboration tools like Yammer. Business groups have an average of 15 people, while family groups have about 10.

As for revenue numbers? Negligible. The company is only starting Google AdSense revenue sharing and talking about business accounts.

Posterous has raised about $5 million in funding from investors including Redpoint Ventures, Trinity Ventures, SV Angel, Founder Collective, Lowercase Capital and Y Combinator.