If your community supports it, you can post new content simply by sending an email to the community. This can be especially handy for posting when you can't reach the community using a browser. For example, you can email content from a cell phone that sends email.
Each place in your community -- from spaces to projects to groups, for example -- provides email addresses for the content you can post via email. By sending email to the address corresponding to documents in the place, for example, you can create a document there. Use the email addresses for the specific content you want to post. The subject line of your email will be the document's title, while the email's body will be its content body. Except when it comes to changing your personal update where you only need to fill in the email's subject line because it's such a small post.
To create content with email: